What could POSSIBLY compel a party to actually accept the mantle they are being given? They get to babysit kids whom the parents KNOW to be troublemakers, and they have to pay for any damages they cause? Simply by saying that as DM, you let the players know that damages WILL be caused, and therefore it will cost the party money to take the job. With a setup as described above, my guys would say "thanks but no thanks."
But, the idea is workable if you have a need of the parent's help in some way(they have information, the PC's need an ally, etc). So, 3/5. Go to Comment
Even though I agree with Strolen, that the idea is something I would use as an annoyance rather than a plot itself, it's still a pretty good idea.
You have some seemingly innocuous incident of finding some insect riddled corpse in the den of some man eating monster or something(take your pick of man eating monsters), so that the necklace doesn't appear to be the cause of the insect horde. The sort of thing that would appear to be a random encounter, only not really random. After defeating the random encounter, they search the body, oh my, what's this, a fancy necklace, thank you very much mr dead body!
Then you continue them down the path of an adventure. At some point in the adventure, typically a fairly critical but non-mortal point, a spell fails because the wizard couldn't concentrate enough to learn his spell correctly. Then it happens again, after another night, soon, he's not able to learn spells at all, because of all the bugs waking him up over and over again in the night. Same thing could happen for a priest learning spells. Maybe the warriors get tired from lack of sleep and can't hit effectively.
MAYBE they get so tired that paranoia steps in. Everyone is out to get you, even your own comrades. Well, maybe, but I find plots like that tend to be annoying for the players in a cooperative group. Just a thought, I suppose.
Of course, you need to have it happen that the necklace is not suspected for a while to get much play out of it. Go to Comment
The PCs accidently start a fire and are caught by the local law enforcement. Since it was accidental, the punishment for the PCs is to fight the fire. Providing they can put it out before it burns down the town, they will not face any further punishment.