Exactly what I was saying Simsane...They'll do what you praise them most for. Also Arthur put the nasty candy in the store as a way to scold them without harming their happiness level. They're healthier when they're at their happiest.
I love it when they write on the walls, play in the dirt, or anything else that makes them giggle and laugh. I love to hear the laughter of little kids.
With the pimple thing; I just move them away from the mirror when they start doing that which seems to result in their doing it less.