Umm - just a thought here, but why not talk to the parents? If they care anything about what their kids are up to, let them know that their son's behaviour is unacceptable.

I caught an 8 year old girl knocking on our front door, then running away. Knocking on our front door, then running away...etc etc. I was walking up the street - my poor spouse kept answering the door. I walked up there PDQ and told her to take me where she lives, *right now*. which she did. When she walked into her house, I knocked on the door. Her mother came to the doorway, I told her what she was up to, and she said, "I'll sort it". It never happened again.

Granted, some parents don't give a crap, but what if they do? They should know, give them a chance to sort their own kids out.