All over the world, parents and their infants play peek-a-boo. The words and the vocal melody of the game are different in Swahili and Polish, but the rhythm, dynamics, and shared joy are the same. In some languages, the standard “peek-a-...” consists of nonsense sounds (bobbi bobbi in Italian & inai inai in Japanese), while in other languages the words are meaningful. For example, in Brazilian Portuguese, a mother playing peek-a-boo sings "Ma-m-a-a-a", while the father uses "Pa-p-a-a-a."
The game follows the same basic format everywhere it's played: the caregiver gives an alert call to summon the infant's attention, followed by a high-pitched release call to accompany their reappearance. The surprising durability and cultural universality of peek-a-boo is a clue that it taps into something fundamentally human.
Peek-a-boo is a powerful learning tool that teaches infants about things like turn-taking, object permanence and emotion regulation. Some have even theorised the peek-a-boo is the foundation for humour as it uses the basic structure of all good jokes—surprise, balanced with expectation.
This seemingly simple game helps infants develop intricate and highly structured expectations over the course of many repetitions. Infants learn to form these expectations by experiencing the relationship between their own behaviors and subsequent events. Research shows that infants are sensitive to these relationships from very early on, responding more vigorously when their own behaviour makes something interesting happen.
As children develop, the cognitive challenges of peek-a-boo changes, meaning a child can go from a passive observer in young infancy to an active initiator and innovator in the toddler years. By adjusting the gestures, words, and tempo of the game it can be skilfully modified over time and adapted to the developing abilities and interests of the child. This is why peek-a-boo is able to be enjoyed by six-week-olds, six-year-olds alike!
References: Fernald & O'Neill (1993); Montague & Walker-Andrews (2001)