In reply to youwillfindjimbo:
Like you say prevention is the key - first all your scenarios carry the caveat "they are children and can't be left" which means you need another adult, second you need to address each problem with the choice of venue:
(1) Don't have a climb where they can refuse to come down (ie finish on steep ground not a ledge). As the question is put you must have known in advance it was possible for the client to refuse to come down so you choose badly in the first place hence "I know the crag and wouldn't choose this route for this group".
(2) Choose somewhere where the rope won't become jammed. Again the way the question is put you know the venue so you choose badly. "I know the crag /route and realise the possibility of the rope jamming so I wouldn't use it for this group"
(3) Don't have a ledge. In the question the ledge is obvious so again you choose badly. Don't choose badly.
The devil's advocate can always wangle the question so that you are forced to leave the group with enough "what-ifs" and a handy way to deal with this is the first point (a spare adult) and to know how to turn your group into a ground anchor which (a) gives you a ground anchor and (b) ties your group up preventing them from wandering off.
Don't over complicate the answers, keep things simple. Within the limits of the SPA you are expected to be able to say you wouldn't do certain things, eg "(q) would you teach lead climbing to a group of novices on a crumbly tidal sea cliff? (a) no" has a mirror "(q) you set up on a unsuitable venue and run into problems something goes wrong what do you do? (a) I wouldn't set up on an unsuitable venue". Suitable venues and planning lend themselves to problem solving.
Any question which fits "You do something stupid and run into problems what next?" gets the answer "I wouldn't do something stupid".
Ultimately you summon mountain rescue and keep everyone safe but this should be reserved for situations when planning or simple fixes can't reasonably be expect to cope.