I will tell them that there is a "Good Fairy" (and I'm not spelling it 'faerie', even if I am Celtic. Suck it down) and an "Evil Fairy." At the end of the day, the Good Fairy will come, "collect" all their good deeds, and leave them money accordingly. Then the Evil Fairy will come, collect their evil deeds, and... uh... leave them money. But it will be EVIL MONEY; every toy they buy with it will be really crappy and probably break, possibly injuring them.
This should teach the surviving children to be good, or at least not overtly evil. And hopefully, the Good Fairy will visit grownups, because otherwise I don't know how I'll be able to afford all this.