That's what we teach in the Junior Duner sessions... we give each participant a bag and tell them that every time they come out to visit, on the last day of their trip, they have to go through the whole camp and go as far as their mom and dad say it's okay to go, picking up all the little pieces of trash no one else seems to notice.
We remind them that when we are gone there are other animals that live here and we have to take care of them so we can come back and visit.

They always take this task very seriously.
Vicki