Fun with shadow puppets! You can do these with kids of all ages. I did them with two and three year olds. While the cognitive ability to figure out the idea of the shadow, etc, was very different, everyone still had fun doing them.
Can foster exploration of light, colour, form, texture and so on. Drawing in a light layer of sand on a light box is quite an experience for children too. All about bringing a sense of wonder to the learning environment.