Either way it is very disturbing and possibly worse if the two of you are friends because then it seems even more deliberate and potentially more premeditated. I'm gonna be honest, nobody messes with my kids. Blood over friendship every time. Go to the police, give them the video and ask them to talk to him, look at his past and ask other neighbors about him. If he's a friend go over and tell him that you felt you had to involve the police because it looked very suspicious, it was your kid's window and it scared your wife and kids so you have to take action to make them feel safe.

Ask for an explanation and unless it makes perfect logical sense say "Sorry if its a misunderstanding but its not about you or me, its about my family. Knock next time."