Demonstrate how light rays travel with this experiment for young children. Light will move in a straight line unless a material that it can't travel through blocks it. Then the light 'bends' and moves off in another direction.
What will happen when you shine a flashlight on different materials? Will light pass through or bounce off and go in a different direction? Have your children make a prediction about each material. Then, to test their predictions, hold each object, one at a time, a few feet in front of the wall. Shine the flashlight at the object (towards the wall). Observe what happens. Does any light reach the wall? Is it less light than without the object in front of the flashlight? Discuss how light can pass through some materials but not others. When light rays cannot pass through a material, they bend and go off in another direction. Can you see the light bending away from any of the materials that block it?