In reply to Krisk:
It depends on the age of the kids.
There are a number of 3's, 3+'s and 4's at Tintern Quarry on 30 Foot Wall.
However there is with Tintern Quarry the caveat that helmets should be worn due to there being some loose rock.
30 Foot Wall isn't as bad as some other areas, but it still has some loose rock.
It also has the advantage that you can access the lower-offs from above, to put up top-ropes.
Mind you, it really does look like a moon-scape quarry.