Some psychologists think that by as early as 3 months old babies will begin to understand that things still exist even when they cannot see them. This is called “object permanence” and is a vital milestone in the way babies understand the world.
You can play games where you hide toys or balls under a cup or hat and then allow your baby to ‘find’ the hidden toy. He will love to lift and move the obstacle to find the toy, that he knows is there. This will show you that he understands object permanence.
Peekaboo is a nice variant of this game where you hide your face and then abruptly reappear. Your baby loves to look at your face and is thrilled to see you reappear!
Peekaboo helps your baby to learn that even when he cannot see you, you still exist. This is a very important concept for when you need to leave him with somebody else. He will start to learn that you will be coming back – and these sorts of games reinforce that idea.