Flashlights. Having two is probably best, but you can alternate using just one.
Dim the lights so that the beam of a flashlight is visible. If your child is older, you can offer him a flashlight and take turns playing "tag" with the spotlight. You can make hand puppets, or experiment with the shadows created by placing different objects in front of the beam. With children just learning to speak, you can shine the beam onto different objects and ask, "Is that a clock?" or "Is that a kitty?" Use your imagination to create your own flashlight game!