Well the thing is that kids will be kids and I daresay you were the same at that age being boisterous as most of us were. You might have a quiet word with your neighbours and explain your concerns, but I'd imagine that they'll see it that you are trying to spoil their garden for them , just as you think they are spoiling your garden for you. It's really very hard, but I'd go softly softly if I were you as I think a big eruption about it will only have consequences contrary to those you'd wish.