Knowing that an object still exists, even if it is hidden, is one of the key milestones in a child's first year. This is known as object permanence and underpins many later skills. The traditional way to play peekaboo is to cover your face and reveal it again, usually to gleeful squeals from your baby, who is delighted to find that his mummy or daddy’s face hasn’t disappeared after all. Once they come to understand that you are hiding, then the joy of peek-a-boo becomes all about the anticipation of when you're going to re-appear. You may find that the longer you leave it, the greater the fun.
All of which adds the value of interaction and language skills to a game of peek-a-boo. It also begins to develop the idea of humour and laughter - vital for advanced human interaction like imitation and eye-contact.
To take peek-a-boo to the next level, and improve your child’s grasp of object permanence, hide a favourite toy under a blanket and encourage them to seek it out. Later on this simple game can become hide-and-seek.