Most people don't care enough to make a difference. Most people aren't going to buy that new thing you're selling. Most people are afraid to take action. Most people are too self-involved to do the generous work you're hoping for.
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.