No snottyness there at all Limey!! Good on you I say.
I've tried soooo many different tactics with clients kids its not funny.
I agree with be-bop, scare tactics usually work (if the parents arent interested), so long as the parents dont hear you telling their kids something awful might happen to them
We had a little bugger picking up handfuls of rocks and piffing them willy-nilly in the yard the other day, I got a dirty look from Mummy when I asked him not to do that because he would damage the cars. I really only said it to let her know that SHE should be doing something about it.