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.
Attention all my preschool teacher friends - Fish craft! Thanks to magnets hidden under the lid, this goldfish shimmies, quivers, and floats in its jam-jar bowl just like the real thing. way better then real fish!