The children in art class experience what it's like to draw with their feet and mouths (and elbows! This is not only a fun, action art experience, but it gives them a new appreciation and gratefulness for their hands.
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.