Pretend to be pirates! Ask your child to look through an empty kitchen roll tube. What can they see? Now bend the kitchen roll tube in the middle and look through it again. Can they see anything? This demonstrates that light travels in straight lines. Light cannot travel around bends.
Place a torch on a table in front of a wall and make shadow puppets with your hands. What is happening? Your hands are blocking the light from the torch. What happens if you move your hands closer to the light source? Does the shadow get bigger or smaller? Try placing other objects in front of the torch such as a mirror. The mirror both reflects the light and causes a shadow because it is opaque.