Attainment of developmental milestones is almost a competitive sport for western parents, particularly American parents who are instructed to put newborns face down on the floor multiple times a day with increasing duration despite many newborns’ vociferous protests. It’s called tummy time and babies need a lot of it to learn how to crawl.
Parents, like Melinda Wenner-Moyer writing in the New York Times, couldn’t stand to force her newborn to suffer through tummy time but worried that in holding her baby instead, she might be setting up her baby for lifelong cognitive, social, and physical problems. Her fear stemmed from the fact that in many western cultures, crawling is considered an essential developmental milestone required for everything from the development of depth perception to spinal maturation, to learning and walking.
But what if instead of requiring active encouragement, developmental milestones were simply the natural progression of ageing in a healthy child, like growing teeth?
In this article, we’ll examine the developmental milestone of crawling in different cultures and in history to answer the question of whether crawling and the associated tummy time, is developmentally necessary or an activity that’s dependent on culture.
Table of Contents
- Developmental Milestones
Developmental milestones cover social, cognitive, and physical categories, for example, babbling in response to other people, rolling over, or smiling. The purpose of milestone calendars is to help parents and caregivers, including doctors, recognise signs of physical or mental problems as early in life as possible so that treatment can be provided. For example, a child who isn’t reaching milestones for their age bracket or a baby who seems to “unlearn” milestones should be seen by a medical provider to rule out underlying conditions.
The AAP suggests that babies should start crawling between eight and twelve months, but gives parents a crawling styles article under the four to eight-month age category…
[Update: in February of 2022, the CDC (working with the AAP) updated their infant milestone calendar for the first time since 2005 when they began the “Learn the signs. Act early.” program, primarily intended to screen for autism and developmental delays. They wanted to make it more in line with what doctors are looking for with regards to delays, so all of the milestones for a given age range changed from 50% to 75% of what babies that age are able to do, and if your baby can’t they suggest seeing a doctor about it. They also removed crawling as a milestone altogether because it’s so varied, with such a wide age range and because a lot of babies skip it. I’m curious if this will change attitudes about crawling, so far it doesn’t seem to change recommendations for tummy time.]
If you’re a parent in North America or Western Europe who regularly uses infant carriers you might have heard the incredibility original critique, “they’ll never learn to walk if you carry them all the time” (which is positively delightful when coming from someone pushing their able-bodied preschooler in a stroller). But the comment underscores the cultural concern that a child who is carried a lot isn’t getting adequate tummy time to learn how to crawl and therefore won’t learn how to walk.
Tummy time was originally developed in 1994 after the Back to Sleep program was implemented in order to prevent torticollis (head tilt) and plagiocephaly (flat head syndrome). Infants who were not placed on their stomachs to sleep rarely experienced a change in positioning day or night, simply being moved from one reclined supine holding device to another, and so developed muscle imbalances causing head tilt or a flat spot on their heads.
It wasn’t until the late 90s that tummy time became associated with developmental milestones. In a 1998 study on the developmental delays caused by the Back to Sleep program, the researchers found that despite significant delays in rolling over, sitting, and crawling in the supine sleepers, compared to prone sleepers, all the infants learned to walk at the same time.
Because there does not seem to be a difference in attainment of the walking skills or of some of the 18-month-old milestones, this difference in milestone attainment may be transient.Davis, et al, 1998
A later study, in 2008, found similar results. Babies with more “prone to play” time (tummy time) developed prone milestones such as rolling over and crawling sooner, but it made no difference to the development of non-prone milestones like walking.
In other words: infant development is not a race, a baby doesn’t gain any advantage being the first baby in the mommy cult to start crawling, they’re all going to start walking at around the same time. Regardless of what the research showed, the transience of developmental “delays” was ignored and tummy time rules supreme.
The importance of tummy time for learning to crawl is emphasized by medical professionals and organizations: the American Academy of Pediatrics recommends placing newborns face down on the floor multiple times a day starting with three to five minutes at a time and increasing the duration so they’ll learn to enjoy it, then, of course, learn those milestones.
The National Child Network, a medical organisation based in Ireland claims that if babies don’t get tummy time or crawl enough that their spine won’t develop the proper curves required for sitting and walking.
Shetland Children’s Physiotherapy Service (via UK’s NHS Shetland) published a pamphlet on the dangers of walkers, which glossed over concerns about injuries to focus on the developmental delays that they are associated with: every hour in a walker results in a three to four hour delay (up to a three to four day delay) in learning to walk compared with a tummy time baby. They write,
Encourage Tummy Time as much as possible – we advise that baby’s should sleep on their backs and play on their fronts. Tummy time is the basic building block for all motor skills and a lack of this can have a huge knock on effect.
They go on to claim that being held in an upright position hinders brain development:
Baby walkers hinder or in severe cases, prevent the child from crawling and keep the child in an upright position which interferes with the natural brain development of the child.
The brain works in a criss-cross pattern with the left brain controlling the right arm and leg and the right brain controlling the left arm and leg. Crawling is an essential activity in encouraging this criss-cross pattern in the brain to develop.
In a walker, [i.e. not on the floor] babies loose opportunities to learn important motor and perceptual skills such as distance and depth, and key concepts such as in/out and on/under.(original source’s emphasis)
Multiple articles suggested that even delayed crawling could be a sign of autism while giving tips to ensure your baby learns to crawl as soon as possible, with similar suggestions for lots of supervised tummy time, exercises, or special garments and toys to encourage crawling. While it is important to identify conditions like autism as soon as possible, many sources framed the issue as though good parents can prevent autism by ensuring plenty of tummy time which will ensure having a baby who crawls “on time” therefore avoiding autism.
When someone has something to sell, crawling becomes even more important. An inventor of a crawling garment designed to provide friction for babies who are learning to crawl on hard surface flooring, had this to say about the importance of creating the perfect environment for crawling, so that the baby isn’t discouraged:
“[…] there is an increased risk of the infant becoming a non-crawler. This in turn provides an increased risk in the child developing Neurological Delay which can lead to behavioral problems and learning challenges being identified in children of school-going age. This can and will have a huge impact on the rest of the child’s development. […] Neurological development is sequential and it is vital that infants are provided with the right environment to support this. The impact of missing a stage in early development is hugely significant. Not only does crawling benefit neurological development, but it also allows for social and emotional development of the infant.”Obesity, Fitness & Wellness Week, 2016 (punctuation and grammatical errors from original)
In Sunil Agrawak’s article in the journal Mechanical Engineering (about creating robots to allow disabled infants the experience of crawling) he claimed:
“In the process of independent locomotion, infants undergo major changes in perception, cognition, and social and emotional development. Studies have shown that the rhythmic pattern involved in moving arms and legs in a coordinated manner impacts the way the developing brain grows and the ease with which it learns. In many ways, crawling is what helps turn babies into children.”Agrawak, 2011
What would happen if a parent carried their baby all the time and never provided an opportunity for tummy time and never encouraged their baby to crawl? The previous sources claim that a non-crawler won’t ever become a child, or that they will be a severely disabled child who is unable to walk independently with an underdeveloped spine, no depth perception, plus learning disabilities and behavioural problems.
We can test these claims by looking at modern cultures with different ideas about crawling and see what effect, if any, this has on their babies’ development.
Central Anatolia, Turkey 1980s
In Judy DeLoache’s and Alma Gottlieb’s book, A World of Babies, they create imagined child care manuals for different cultures and time periods based on historical or ethnographic research.
In Anatolia, babies are not generally allowed to crawl around because it’s thought to be too dirty and unsafe. Plus it is disruptive to the running of the home to have to pay attention to a mobile baby on the loose. Instead, babies are almost always being held by someone.
“Most of the time babies are held by someone; we don’t usually let them crawl around very much. Indeed, I am not sure all babies even learn to crawl. They are hardly ever put down on the ground outside, because it is just too dirty and they might pick up something dirty and put it in their mouth. In the house, you can let them sit and crawl around on the floor from time to time because the floors are swept clean several times a day. They will find all kinds of things to play with, but you must be careful– I have seen babies playing with knives and scissors, and that can be very dangerous.”DeLoache and Gottlieb, 2006
Rajputs of Khalapur, India 1960s
In the Six Cultures collection on child rearing, psychologist Leigh Minturn and anthropologist John T. Hitchcock were part of Cornell University’s Cornell India Project. In their ethnography they describe attitudes about crawling in the Rajput culture of Khalapur (southwest of Mumbai) in the 1960s:
“A baby spends little time crawling. Sometimes, unattended, he may set off across the courtyard on his own, but someone usually grabs him before he gets far. Since the women do most of their work on the floor, the food dishes, grain dishes, and so on are usually lying somewhere. This makes a crawling baby something of a nuisance, although there is little that can hurt him except the hearth fire and an occasional spinning-wheel spindle or knife. If the infant is crawling toward some area where it is not supposed to be, or playing with some object which it is not supposed to have, an adult simply removes either the baby or the object rather than attempting to coax the baby to give up the object or to crawl away.”Minturn and Hitchcock, Six Cultures, 1963
If the baby is being stubborn about getting into trouble, such as returning to something they’ve been removed from adults will use physical punishment, like slapping the baby. So not only are babies prevented from crawling, they may even be punished for it.
Taira, Okinawa, Japan 1960s
Another contribution to the Six Cultures collection was Thomas and Hatsumi Maretzki’s study of Taira on the northeast coast of Okinawa, in 1960s Japan.
In this culture, infants are nearly always carried on the back of their siblings or grandmother and crawling is not allowed, because ain’t nobody got time for that.
“In spite of the fact that he is capable of crawling or learning to crawl within the second half year of his life, he is kept on the back. He does not protest or clamor to be put down; he seems to prefer being carried to being left to crawl.”Thomas and Hatsumi Maretzki
“Caretakers are too busy with work or play to let the child crawl about freely, so there is no crawling stage in Taira. Older siblings are too involved in play to sit and patiently watch a crawler.”Thomas and Hatsumi Maretzki
In fact, the only children who were allowed to crawl were those of wealthy fisherman’s wives, who didn’t have chores or work to do. They had the leisure to sit and watch their babies crawling and an environment that made it safer. Average farmers in Taira lived in elevated houses, a central hearth and living spaces that were opened to the wrap-around porch with loose floorboards.
“A mother who sits and plucks sweet potato leaves off the vines for hog feed works more efficiently with the baby on her back. Crawling around on the loose floorboards near the fire pit or over the edge of the raised floor, the child would require constant attention.”Thomas and Hatsumi Maretzki
In this environment, there was no floor time or ability to practice crawling, and certainly no encouragement from caregivers, yet the infants still knew how to crawl. In fact, there were many stories of infants taking off crawling the moment they were removed from their strap carry, much to the horror of their caregivers:
A big sister was playing with friends with the baby strapped to her back. The baby was tall enough that it could touch the ground with its feet and bounce, causing big sister to lose her balance while she was squatting to play. After unsuccessful attempts to get the baby to stop, the big sister unstrapped the baby and let it crawl. Another kid cried out that the baby had eaten dirt and the big sister, knowing she’d be severely punished for taking the baby off her back, rushed over to flush out the baby’s mouth and put the baby back on her back.
Another time, a mother was working with sharp bamboo and a knife to make baskets when an older sibling brought the baby in for nursing. The mother pushed away the sharp objects to feed the baby. When finished she put the baby down and called to the older sibling to take the baby away, but the child had run to get a drink. The baby went for the knife, the mother grabbed it away, and then the baby went for the sharp bamboo. The mother had quite enough of that and yelled at the kid to come get the baby on their back and to go play.
Another kid put a baby down in the courtyard of the grandmother’s house because it was the grandmother’s turn to carry the baby. In a few unsupervised moments, the baby peed on the ground and then crawled around in the urine mud. The grandmother came out to find a filthy baby, she was disgusted that the child let the baby crawl, and upset that she had to bathe the baby before strapping it on her back and going about her day.
Another entry in the World of Babies was from Bali, in Indonesia, a culture famous for never letting a baby touch the ground for the first 108 days after birth when the Nyabutan ceremony is held marking the first time the baby’s feet touch the ground.
“During the day, your baby will be carried by someone most of the time, even after he or she can crawl; it is base for a baby to crawl on the ground like an animal. Hold the baby in your arms or in a sling around your body as you go about your daily business. Your infant can stay in the sling even while asleep, although you may want to pull the cloth over the child’s face. If you have put your child down to do some work, another person- your husband, a sibling, child caretaker, grandparent, aunt, uncle, cousin, or neighbor– should hold the child. Everyone loves to hold a baby.”DeLoache and Gottlieb, 2006
Warlpiri of Central Desert Australia
Also in World of Babies, Sophia Peirroutsakos shares the advice and experience of Old-Law Warlpiri culture she gave to her granddaughter. The Warlpiri are an aboriginal culture living in the Central Desert in Australia.
“Before returning to your daily responsibilities [after birth], you will need something for carrying your infant. In my day, we used an oblong, bowl-like baby carrier carved from wood, called a parraja or a coolamon, lined with blankets. Shoulder straps attached to the ends allowed me to carry my baby comfortably along my side. I found this helpful as I did my chores.”Sophia Peirroutsakos,”World of Babies”, 2006
“You should hardly ever put your baby onto the ground; instead, you or another person should hold the baby most of the time. I find it unthinkable to leave your baby alone! If you are a young mother, other women should keep an eye on you to make sure you do not mishandle your baby.”
“Toward the end of the first year, babies begin crawling and walking, even if we could keep them in the wooden sling, they would have outgrown it. In the old days, at this point, it became difficult to bring the child along to search for food. Our husbands were often hunting during the day; in any case, they were not usually responsible for young boys or for girls of any age. Fortunately, we could count on our female relatives for help. When we needed to gather food, we could leave our child with our sisters, mothers, or grandmothers. Of course, there were times to reciprocate and look after their children while they collected food.”ibid
In this culture, crawling was discouraged, in fact, leaving your baby on the ground was considered mistreatment. But they recognized that at some point the child is going to be too big and active to be carried or otherwise prevented from crawling even though it presents a problem for foraging. So they use what’s known as cooperative breeding strategies in which members of the community care for each other’s children, taking time away from gathering food, to ensure everyone’s survival.
Beng, Côte d’Ivoire, 1990s
In the early 1990s, researcher Alma Gottlieb stayed with the Beng people of Côte d’Ivoire (Ivory Coast) in West Africa. In her book, The Afterlife Is Where We Come From, she described their ideas about crawling.
Beng babies are allowed to crawl but they need to crawl with their bellies up:
“[…] creeping or slithering with the belly on the ground, rather than crawling with stomach raised, is considered unacceptable by Beng parents, who do all they can to reorient a baby who seems inclined to slither rather than crawl”Gottlieb, pg 129
This slithering crawl is considered a bad omen, a “tɛtɛ,” which can include infants whose development is not in line with cultural norms. For example, an infant with teeth before age one or a baby that starts crawling later than other babies their age. These kinds of bad omens are associated with the death of an infant’s relatives.
To encourage correct crawling, a Beng mother may locate a left-handed person who then finds a shrub growing on a mound. Both left-handed people and hills are considered to contain mystical powers, though in opposite directions, inauspicious and auspicious, respectively. The left-handed person uproots the plant and gives it to the baby’s mother, who crushes it well with chili pepper and uses it as an enema for her infant.
“Perhaps their combined powers are seen as having an effect on accelerating a baby’s motor development.”Gottlieb, pg 126
Beng babies get dirty crawling in the dirt but they are bathed twice a day until they learn to walk independently.
Wogeo, New Guinea
In Barbara Rogoff’s book, The Cultural Nature of Human Development, she describes the attitudes towards crawling and walking in Wogeo, New Guinea, and how cultural practices affect the development of infant mobility.
“In some communities, walking sooner is valued; in others, it is not desired. In Wogeo, New Guinea, infants were not allowed to crawl and discouraged from walking until nearly 2 years of age so that they know how to take care of themselves and avoid dangers before moving about freely. An infant who showed an interest in moving about would be immediately picked up or put firmly in a corner. Toward the end of the second year, children learned to walk well within two or three days.”Rogoff, 2003
Photos from left: Melanesian Villagers in Jayapura, Papua in 2004 by Mangiwau; Mother and baby in Pot Moresby by Clyde Lovuru/EyeEm; Papuan Family also by Mangiwau.
Rogoff quotes an excerpt from Hogbin’s 1943 publication on infant development in New Guinea:
“No one seems to think that active encouragement of any kind is necessary. When I told the natives how we coax our babies to stand at a much earlier age, they admitted that such methods might be suitable where there was no fireplace or veranda from which to tumble, but they openly laughed at me for speaking of ‘teaching’ children to walk. A child walks of it’s own accord, they said, once it has reached the appropriate stage of growth; I would be saying next that trees had to be instructed in how to bear fruit.”Hogbin, 1943, p 302
“Differences in communities’ values and expectations underlie varying parental efforts to help children learn skills. African infants routinely surpass U.S. infants in their rate of learning to sit and to walk, but not in learning to crawl or to climb stairs. This may be because African parents provide experience for their babies that are intended to teach sitting and walking. Sitting skills are encouraged by propping very young infants in a sitting position supported by rolled blankets in a hole in the ground. Walking skills are encouraged by exercising the newborn walking reflex and by bouncing babies on their feet. But crawling is discouraged, and stair-climbing skills may be limited by the absence of stairs.”ibid
Olmecs, Central America
In doing research for this subject, I looked for the earliest depiction of infant crawling in art history, there isn’t much, but there are the Olmec infant statues, one of which is crawling. The Olmec culture had a tradition of creating life-sized infant statues dating from 1200 to 800 BCE; the civilization as a whole flourished between 1500-400 BCE and is famous for its colossal basalt stone head sculptures.
It is unknown if the infant statues represent an idealized form of infanthood or if they represent actual high-status infants. They are believed to have been used as effigies of real infants in sacrificial rituals. James Doyle of The Met Museum writes,
“In some cases, the ceramic effigies may have served as substitutes for actual infants in a sacrificial or dedicatory ritual, as there is compelling evidence of Olmec infant sacrifice or ceremonial burials.”
Sites containing infant statues made of wood or clay have been discovered to also contain infant remains, for example, wooden busts and infant remains were found at the El Manatí bog.
Child sacrifice is never a pleasant subject, however, the point is that the ancient Olmecs placed infancy in high regard. Some Olmec infants, perhaps only high-status infants in control environments with attendants to supervise their safety, were allowed to crawl, and the crawling stage of infancy was valued enough to be immortalized in their art.
Allowing infants to crawl around is a relatively recent trend even in western cultures. Throughout western history, crawling was seen as animalistic, and along with other animalistic behaviours, the role of a good caregiver was to break the child of (or prevent) such bad habits. From ancient times, infants were swaddled and strapped into cradles until they were old enough to be put in sundry baby holders or walkers. The ideal environment for a swaddled baby was one with a minimum of physical or mental stimulation and that idea persisted into the 20th century and continues in some western cultures to this day.
Less than a century ago, in 1929, the Infant Care booklet published by the Children’s Bureau in the United States recommended keeping babies off the floor using baskets or playpens to avoid dirt and germs, and dangerous items like fireplaces or radiators. Holding the baby was to be limited in duration and carrying was recommended against, both for over-stimulating the baby and for fatiguing the mother.
The booklet also warned parents not to help babies stand or encourage them to walk before the baby was “naturally ready” (i.e. doing it of their own volition) for fear that if held in a standing position prematurely, their body weight would cause bowed legs. If you feel yourself getting anxious, don’t worry, this isn’t true, but this goes to show how a culture’s ideas change through time.
The generation of American children who came of age in the 1940s were not encouraged to crawl and were emphatically not encouraged to walk. Remember all the terrible consequences today’s parents are warned about if their baby doesn’t get enough tummy time to learn to crawl: did westerners suddenly begin walking upright, developing depth perception, and maintaining balance with the invention of central heating and wall-to-wall carpeting? No.
The difference between modern crawling cultures and non-crawling cultures is the amount of holding and carrying a baby receives. In terms of infant development, tummy time is the slightly inferior version of being held and carried. Both tummy time and carrying provide mental and physical stimulation (and prevent torticollis and plagiocephaly) but carrying also provides social learning which is lacking down on the floor. But being on the floor is vastly superior to the western alternative to tummy time, which is keeping infants in restrictive holders in a reclined supine position (on their back), like a car seat or an electric swing/rocker.
Medical professionals promoting tummy time may not even recognize that holding and carrying is an alternative, and are unlikely to recommend something they do not believe patients will adhere to or do safely. Plus, much of the scientific research on the benefits of crawling does not compare tummy time/crawling infants to carried/non-crawling infants but instead compares crawlers to neglected or disabled infants.
Milestone calendars are a valuable diagnostic tool but where they fail is, first, in promoting cultural ideas about infant development as universal biological norms; second, in promoting the idea that the milestones require active encouragement to develop; and third, there is confusion about whether milestones have “knock-on effects”. For example, babies develop better depth perception around the time they would be physically capable of crawling, but that doesn’t mean a baby who doesn’t or can’t crawl will fail to develop depth perception.
In addition, the consequences of conditions that milestone calendars are intended to help screen for are often portrayed as consequences of not teaching one’s baby milestone skills. For example, a child with cerebral palsy who isn’t crawling may never be able to walk, but not being able to walk wasn’t caused by not learning to crawl, it was caused by cerebral palsy. No amount of tummy time or encouragement to crawl will prevent or correct cerebral palsy, or autism for that matter.
Individualism vs Collectivism
Another angle I would like to explore is the ideas of individualism versus collectivism between crawling and non-crawling cultures. Western cultures tend towards individualism whereas other cultures teach children that they are part of a community, a collective. I have heard people in non-crawling cultures say that they find front-facing strollers and carriers disturbing because it implies that the baby is expected to lead, to face the dangers of the world alone, ahead of their caregivers, and that they say is contrary to the baby’s nature: a baby’s place is on the back of someone who will care for and protect them.
Many of the purported benefits of crawling are about the independence of the act, but quadrupedal babies are still too young to recognize danger, let alone defend themselves, and this is why so many cultures will not allow a baby to crawl. Beyond crawling though, how much of western infant care is hung up on the idea of a baby being independent: sleeping alone, feeding themselves, and even entertaining themselves; where does independence become loneliness?
The other major difference between crawling and non-crawling cultures is the amount of and access to child care. The non-crawling cultures had babysitters in droves, children as young as five, friends, neighbours, and relatives including the baby’s older siblings and grandparents were all ready to hold and carry a baby around, sleeping or awake, so that mothers can go to work. And that is a very prescient point: in none of the non-crawling cultures were mothers the exclusive caregiver, they all had work to do and no one expected them to do it while carrying their baby.
Meanwhile, American child care sucks. Full stop. There are many complicated reasons for this, but in brief, childcare is extremely expensive so the majority of families who need childcare will seek a daycare because a private nanny would bankrupt them and relying on family members isn’t always feasible or desirable.
In a daycare, at least at a licensed facility in the US, ratios must be kept, for example, in a Baby Room, it may be one to four ratio: one adult gets to care for four babies. At any one time, a Baby Room teacher will be juggling a hungry baby while a bottle warms, using a foot to bounce another fussy baby in a bouncy seat, all the while hoping the two babies on the floor don’t use those razor-sharp baby talons to claw at each other’s faces, and omg where is that smell coming from?
If there were still experts warning against putting babies on the floor for fear of drafts, or because it encouraged animalistic crawling habits, daycare babies would spend the entire day in a restrictive baby holder or on their back in a crib simply because the caregivers are out-numbered four to one.
Stay-at-home-parents are usually caring for their children alone too (though that may be preferable to a mother-in-law who berates you for literally everything like in Taira) but just like with the daycare setting, one adult to multiple dependent young children can make it complicated (or undesirable) to hold and carry a baby all day, even without the cultural hangups about holding babies, leaving tummy time or restrictive holders as options. (Just to clarify, there is nothing wrong with using baby holders now and then, it’s more an issue of changing positions and perspectives for the baby’s enrichment.)
There are many cultures that do or did not allow crawling and actively prevent babies from doing so for health, safety, or cultural reasons. The babies in Taira, Turkey, Central Australia, India, and Bali were not allowed tummy time, let alone free range to practice crawling, yet in brief moments when left to their own devices babies were crawling independently as if by instinct. Non-crawling infants grow up and learn to walk around the same age as infants in cultures that do encourage crawling.
Crawling is cultural, it’s dependent on the environment and resources to supervise and protect a baby who is not old enough to understand danger or defend themselves. Being prevented from crawling is not a risk to future development, including walking, so long as infants get plenty of mental and physical stimulation through being held and carried by other humans.
Crawling is not a necessary skill and is incidental in otherwise healthy infants; babies crawl because they can not because they need to. For these reasons, I believe that less stress should be put on the attainment of this transient developmental milestone and holding/carrying recognized as an alternative to tummy time.
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Agrawak, Sunil K. March 2011. “Robots for infants”. Mechanical engineering, 50-51.
Davis, Beth Ellen, et al, 1998. Effects of sleep position on infant motor development. Pediatrics. 102(5):1135.
DeLoache, Judy and Alma Gottlieb. 2006. A World of Babies: Imagined Childcare Guides for Seven Societies. Cambridge: Cambridge University Press.
Doyle, James. 2015. “Olmec Babies as Early Portraiture in the Americas.” Now at the Met. The Met.
Gottlieb, Alma. 2004. The Afterlife Is Where We Come From: The Culture of Infancy in West Africa. Chicago: The University of Chicago Press.
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