I find that the only way to make my characters really interesting to children is to exaggerate all their good or bad qualities, and so if a person is nasty or bad or cruel, you make them very nasty, very bad, very cruel. If they are ugly, you make them extremely ugly. That, I think, is fun and makes an impact.
The fine line between roaring with laughter and crying because it's a disaster is a very, very fine line. You see a chap slip on a banana skin in the street and you roar with laughter when he falls slap on his backside. If in doing so you suddenly see he's broken a leg, you very quickly stop laughing and it's not a joke anymore.