In reply to Steve Brooks:
Check out the small buttress on the left just before you reach Pine Wall Buttress at
Polldubh Crags, Glen Nevis. That's about 15/20m and you can easily walk up the side and fix a top rope.
You could also take them up
The Gutter (D) which is a brilliant Diff if you're looking for something a bit longer, I'm sure they would enjoy it. That's on Pine Wall.