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This question was inspired by At What age does a baby recognize themself in a mirror? and the memory it brought up for me of the day we were on a family "hike" at a local botanical garden and my daughter (age two?) looked down and started flapping her arms. You could see that she was testing if the gray thing at her feet would also flap and when it did, she giggled with glee and started "running" in that cute almost falling way kids do while flapping her arms and giggling at the fact that her shadow was also flapping away.

Obviously my daughter was walking at this point, but I have video of her discovering her reflection at an age when she was "almost" walking but not quite. I wondered if the discovery generally happens in the same range of time or if they are two distinct "discoveries" in terms of cognitive development.

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    Along the same lines, when a child recognizes an echo to be their own. My parents were fortunate enough to have caught me on tape when I discovered my own echo (and the subsequent loud shouts and laughter). – Doc Feb 4 '14 at 16:06
  • This is intriguing... I don't remember the answer for my own daughter. It is very interesting as she asks questions in an effort to discover the universe around her (sometimes in the not-so-right setting), but I don't recall the shadow or mirror. :) – Sylas Seabrook Feb 6 '14 at 7:40
  • My son recently noticed his shadow when he was a year and four months. I don't know how soon in age a child learns of her own shadow, but it appears to be lower based on other answers. – Mea quidem sententia May 4 '17 at 17:48
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My "educated" guess (based on experience) is that a child will generally recognize their shadow is their own during the younger half of age three (36-42 months) My son is almost four, and we have been playing "shadow games" since the summer, when we traced our shadows with chalk in the driveway. On the other hand, my almost two year old doesn't quite grasp it yet. He is aware of the cause and effect though, so he's well on his way. That's the closest I can narrow it to. I hope that helps!

Oh,and by the way, according to my baby journal, my little one was able to communicate that he recognized his reflection at age 17 months. ( Me: who's that? Baby: "baby! " and points to self. It changed to "Me" at age 21 mos.) although, it's arguable that that's not exactly the same as when he was able to recognize himself. How would one know though without reliable communication, which doesn't come until later?

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    Some external references would be nice for this answer. What is your "educated guess" based on? – Dariusz Feb 10 '14 at 10:41
  • @Dariusz : it's based on having two kids at the age where this milestone is reached. The OP couldn't remember, but I can because it just happened for my child, and is close to happening for my other one. – Jax Feb 10 '14 at 12:22
  • "How would one know" --- good question! There are a few standard techniques for testing this scientifically, the most common of which is the rouge test – Rose Hartman Feb 24 '18 at 22:21
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There is a great difference between "recognize" and "understand". Recognizing one's shadow can happen as early as few months old, as this other answer implies. Then at later age, kids can start playing with their shadows, and other people shadows they see.

However, the real question should be: "when children actually understand the concept of shadows?" and my research brought up surprising results. To sum this up, the answer I found is that the concept of shadows is being truly comprehended only during one's adolescence (!), meaning somewhere around the age of 10-15.

The research I found (PDF) is using several books, here are the relevant quotes:

Three years old

For example, three-year-olds often use their intelligence to reason that their shadows go inside themselves when they cannot see them

Five years old

Five-year-olds often believe their shadows are under their bed or covers at night

(Source for both the above: DeVries, 1986; Piaget, 1929/1960)

Nine years old

Even 9-year-olds do not believe that shadows are transitory. Rather, they are convinced that unseen shadows are still there somewhere

(Source: DeVries, 1986)

And finally:

...children construct their knowledge about shadows over a rather long period from age two through adolescence. Correct ideas about shadows are the result of logical deductions that allow the child to correct erroneous ideas

(emphasis mine)

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The answer depends a little on what exactly you mean by "recognize their shadow is their shadow".

The simpler understanding of shadows

If you mean "realize that their shadow matches their own movements" (i.e. that they can control their shadow), then all that's required is for them to 1) see their shadow, and 2) notice the contingency between their own movements and the shadow's.

Seeing their shadow: Young infants have pretty bad vision at any distance farther than a couple feet away, so the age at which they'll be able to see their shadow clearly enough to notice its movements depends on how high contrast the shadow is, how far away it is, and how old the infant is. Newborns would only be able to see shadows that were quite high contrast and almost right in front of their faces, but older infants and children would be able to see shadows farther away and with lower contrast.

Noticing the contingency between their own movements and the shadow's: Infants are actually very good at noticing contingencies, and they are generally delighted by them --- anyone who has given a toy that lights up and makes sound to a baby will likely remember (with a grimace) the constant, repetitive activation of the toy as the baby pushes the button to "make it go" over and over. Babies are surrounded by contingencies, and noticing them is a big part of learning about the world. Here are some examples, all of which you may recognize as favorite games of many babies:

  • drop things and they fall
  • bang things and they make a sound
  • smile at adults to make them smile back at you

Infants are great at noticing contingencies very early on, and they especially like things they can control. Most of the scientific research on infant memory and cognition relies on this fascination for contingencies, in fact.

A classic example is the mobile task developed by Prof. Rovee-Collier. The baby lies down in a crib underneath a hanging mobile, and the researcher ties a ribbon from the baby's ankle to the mobile support. When the baby kicks his/her leg, the mobile will jerk around. Infants as young as 2 months realize this quickly and will kick their legs more than usual in order to activate the mobile. Rovee-Collier and her colleagues designed several clever experiments to test infants memory development using this task. Even earlier in development, scientists can use contingencies between the rate newborns suck on a pacifier and the appearance of other stimuli to test newborn cognition. For example, in a classic study Prof. Morse gave newborns a special pacifier that measured how fast they sucked and would trigger an audio system to play simple speech sounds or other noise depending on whether they sucked faster or slower. Newborns (40–54 days old) picked up on the fact that could control what they heard by sucking faster or slower.

So basically, it appears that babies are sensitive to (and interested in) things they can control in their environment pretty much from birth. In that case, the age at which a baby might recognize his/her shadow and understand he/she can control it would be as soon as he/she gets a good enough visual experience with one. Infant visual development and the availability of a clear, high-contrast shadow is probably the limiting factor in many cases, rather than an infant's ability to notice the relationship between their own movements and the shadow's.

The more complex understanding of shadows

If by "recognize their shadow is their shadow", you mean something more like "understand that his/her shadow is a representation of his/herself", then that's a bit more advanced. Not only does that require seeing the shadow and noticing its movements are contingent, it requires having a sense of "self" in order to recognize that your shadow is an image of you. The sense of self develops slowly over the first several years of life.

A good analogous test is the rouge test used to tell whether babies recognize themselves in the mirror. Typically developing infants don't pass this test until around 2 years. Note that infants much younger than that will notice the baby in the mirror and often be delighted by the fact that Mirror Baby moves when he/she moves --- this is analogous to the simpler definition of shadow understanding discussed above --- but he/she won't realize the fact that the mirror baby is him/herself.

Because passing the rouge test is thought to reflect (no pun intended) a developing sense of "self" rather than anything specific to mirror reflections per se, one would expect an child to be able to recognize that his/her shadow is a projection of his/her body around the same time. It would be a little harder to test than mirror reflections, but you could perhaps put something behind your child's head (not touching it) in such a way that the shadow made it look like he/she was wearing a hat, and see if he/she reached up to check his/her own head for the hat.

If all you're noting is that your baby moves his/her own body in an apparent attempt to move his/her shadow, then that doesn't necessarily mean he or she understands what shadows are in a deeper sense.

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