Play with shadows using your hands and a bright light. A portable lamp or a flashlight will do.
Shine the light on your child's hand so that the shadow of his hand falls on a smooth surface like a wall or table. Invite your child to move his hand closer to the light and farther away from the light. Notice what happens to the shadow.
Have him turn his hand in different ways to see how the shape of the shadow changes.
If your child enjoys this activity, get some crayons and put a piece of white paper on the wall. Try shining the light onto a piece of white paper and trace the shadow of your child's hand as he holds it at different distances from the light. (This may require some maneuvering or another set of hands!)
What does your child notice about the drawings? Can he make your shadow too big to fit on the paper? How small can he make the shadow?