I would have to say that teaching rapelling as a stand alone skill, that is, out side the larger context of rock climbing, mountaineering or caving, to any group or individual is not a good idea.

Giving them an introduction to safe climbing practices, and maybe just a little top rope work might be something that would get their attention, but I am not sure how enthusiastic BSA is about even elementary technical climbing.

My experience with Scout troops has been that they are highly variable, ranging from excellent to a good imitation of barbarian hordes swooping down to sack Rome.