To the Op,
Next time don't call the police while you had them all sitting there, im sure you know this now. You could:
1. Rob them and search for ID... lol If you find ID, take it and give a "threat" if you see them hanging around again you will blah blah blah..
2. Also you could do the classic call there parents on the phone you find then smash the phone in front of them.
3. If they have a watch or some chains/rings or something just f**king take it and say "This is compensation for the damage you have caused to my car"
4. And if they had nothing worth taking just take their shoes... Lets hope there wearing there best trainers! haha
People should add to this list, "What to do when kids throw rocks at your car and get caught"...
Yes I'm a bad example but im sure they will be going home thinking twice about throwing rocks at cars.