Every parent has witnessed the sheer, unadulterated shock on a baby’s face during a game of peek a boo. To an adult, it is a repetitive exercise in hiding behind your hands. To a child under eight months old, you are literally folding yourself out of existence. This hilarious reaction is due to a lack of object permanence. This is the understanding that things continue to exist even when they are out of sight.
During the sensorimotor stage of development, infants are still figuring out how the world works. Jean Piaget, a pioneer in child psychology, noted that babies initially believe that their perception creates reality. If they do not see the ball, the ball is gone from the universe. This is why a toddler might cry when you leave the room but stop the moment you return. They are not being dramatic. They genuinely thought you were deleted.
We have all seen the photos of a toddler hiding during a game of hide and seek by simply closing their eyes or putting a bucket over their head. While they are clearly visible to everyone in the room, they truly believe they are masters of stealth. This is a classic example of egocentrism. This does not mean the child is selfish. It means they lack the cognitive ability to understand that other people see the world from a different physical and mental perspective.
In the preoperational stage, which usually lasts from ages two to seven, children assume that if they cannot see you, then you cannot see them. Their brain is centered on their own viewpoint. They assume that their internal experience is a universal experience. If their eyes are dark, the whole world must be dark. This cognitive quirk makes for some of the best internet fail videos but also represents a vital step in learning how to navigate social spaces.
If you want to win a trade with a five year old, just offer them two nickels for one dime. They will likely take the deal because two is more than one. This logic also applies to the famous conservation experiments. If you take two identical balls of clay and squash one into a flat pancake, the child will almost always insist the pancake has more clay because it takes up more space on the table.
This happens because children at this age struggle with conservation. This is the logical thinking ability to see that quantity remains the same despite changes in shape or container. When you pour juice from a short wide glass into a tall skinny glass, the child is convinced they just got a massive upgrade. They are focusing on only one dimension, like height, while ignoring the width. This is called centration. It is a bug in the young human operating system that eventually gets patched out as they enter the concrete operational stage.
Young children are notoriously bad at lying. If a three year old eats a chocolate cupcake, they will stand there with frosting smeared across their nose and insist they have no idea who did it. They fail at this because they have not yet developed a robust theory of mind. This is the realization that other people have different thoughts, knowledge, and beliefs than they do.
