Too far away to help, however, I have tried caching with a small group of my Scouts (Navigator badge part D). So far a couple of them (those who had a GPS at home) have started to cache on their own.
I am running an Expedition this weekend where I will be introducing caching to 4 more Scouts. I have also bought a cheap second hand GPS for the Troop so it could be loaned out if someone wants to try it with their parents before buying their own GPS.
Good luck with your event. I am sure that most of them will enjoy something different.