Is it possible to make them think you left and catch them in the act with a camera? Or have somebody else do it, if you can't? Have you ever spoken to them about property boundaries? They're young, so it might just take you setting the boundaries- their parents probably aren't going to teach them these things and as this is effecting you, the responsibility has (unfairly) fallen on your shoulders. I'm in a very similar situation with the neighbor kids, who are rather neglected and have no idea what (ehem- property line) boundaries are. They used to show up at our back door randomly in the morning on the weekends and knock for an hour... my room is right next to the door, and frankly I want to sleep in on the weekends, so after a while of this I got up, opened the door, and told them if they didn't call first, they couldn't come over, and if they bothered me again, they would never come over again anyway. Period. They wouldn't come over again for a week, they told my little sister that they were too scared of me. I didn't even raise my voice, talk about looking scary when you wake up... LOL.