Use cardboard, craft sticks, and hot glue to create an epic marble run! The marbles land in paper cups at the bottom of the track. This is a fantastic engineering challenge for kids. How should we position the sticks? Which path will the marbles take? How
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.