Hide and Seek

What to do:

Take a small ball, and place it on the floor in front of a four-month-old. Lie him on his stomach.
When you know he is looking at the ball, move it to his right or left side and place it back on the floor. Watch as he wiggles to turn and find the ball.
Use this same ball to help a five-month-old learn to roll over. While she is lying on her back, show her the ball and make sure she sees it. Slowly move the ball to the right or the left, making sure that she keeps looking at it. She may turn over trying to see or reach for the ball.
Give her the ball to play with.

Variations:

A one-year-old will enjoy another version of this game.
While you are playing ball with him, tuck it in your pocket with a little bit showing.
He will have fun looking for it. A fifteen-month-old will enjoy putting the ball in her own pocket and retrieving it.
This is another lesson in trust and object permanence.