Sorry to hear about that, but I would do either of two things-First follow the police's advice. It is hard to suck it up and forget it, but these are 10-12 year old kids, more than likely as the summer progresses they will move on to something else. Other thing is to do something harmless, but effective-like setting a sprinkler up right near that fence, so when you see them getting close-turn it on full blast! The broader scope of your post I have no easy answers for you. There is a lack of civility here, but also a degree of kids being kids, despite your own honest and decent neighborly attitude for 40 years. Short term in terms of what to do, do as the police said, then re-evaluate.