Any type of chain should work, but ball chains are particularly good. Order them here: www.ballchain.com
They also sell through amazon. Just think, the kids can help you put it back in the jar for the next demo. The farther the chain falls, the higher it jumps up out of the glass. This could be done from the second story overpass by the main gate...
The guy in the videos is worth following for many more ideas: stevemould.com