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.
story stones, hand-painted rocks, childrens literacy, art stones, tell me a story. Cool new idea. Everywhere you go find a stone. Gather the stone(s) and when you get back home paint them to match the memories!