Climbing/bouldering wall. good for any age, kids seem to really like it.
Only use holds on feet where the pennies are placed without knocking them off
Place pennies on a bouldering wall (this could be done on toprope/regular climbing wall, however there will be falling coins most likely so keep this in mind. The participants must traverse the wall using only the holds with pennies on them for feet without knocking them off. It gets them thinking about how to use their feet and shifting weight on the all to improve climbing.