Balloon Rockets - I've done this in several science camps I've conducted. Kids have fun with it. But, when the balloon deflates it may fall off the straw because it's surface area changes - another good thing to show and explain to kids.
Mandala: a geometric figure representing the universe in Buddhist symbolism; a symbol in a dream, representing the dreamer’s search for completeness and self-unity. From: "moment to moment photographic journal of natural living.
Paper Airplane Target practice -- yes! Cut holes in a large piece of paper and have children aim their hand-made paper planes through. Set a certain number of tries, and give a prize to the winner who got the most planes through the holes.