I found this while surfing the net this morning. It's an art installation that was created for the 2007 Cinekid Festival in the Netherlands by a woman named Emily Gobeille. She has her own website that you should also check out!
'Funky Forest' is an interactive ecosystem where children create trees with their body and then divert the water flowing from the waterfall to the trees to keep them alive. The health of the trees contributes to the overall health of the forest and the types of creatures that inhabit it.
Click here to see a cool video of kids interacting with 'Funky Forest'.