Why is it "practically impossible" to take a photograph? At least you would then have some evidence to show them. If the Police had to turn out "Blues and Twos" for every old biddy who thinks that a bit of horseplay by kids is the equivalent of the Toxteth riots, it would fill up their entire shift pattern.
When a group of kid's behaviour becomes threatening or dangerous to others (and themselves) the Police must intervene and will respond rapidly. But this whole thing has to be put into perspective. Have you ever stopped to think that the kid's behaviour isn't getting worse, it's just that you are getting older and less tolerant? Kids have always congregated together, they have always broken windows, egged houses and teased old people. (usually, the older and more miserable the more fun it is). Yes it's unfair and unkind to old people but, when you were13 or 14, did you care whether you hurt some old person's feelings? Kids are, by their nature, cruel little bastards, I should know, I went to school with them. But they do not, for the most part, set out to hurt and terrorise, to them it is a bit of fun.
So, if you really are that worried, take a few photographs and get the Honorary police to have a word with the kids and their parents. Community Policing inside the Parishes is what the Centenniers are supposed to do. Failing that, why don't you complain to your local Deputy?