A couple of times, we planned two congruent trips, with the less-experienced group and adult leaders taking one trail, and the older, more experienced group taking another loop that had them spending a night on their own. Each group knew where the other was hiking and camping, in case some need to make contact arose, but the older ones were really on their own - even though there was only a couple of miles between us. We used a national forest they'd been to before, so they'd feel more comfortable.

They had a great time, and kept going back after they had aged out of the youth group. (A couple even volunteered as adult leaders a few times.)