I haven't read through the entire thread, so I don't know if I'm addressing an already discussed point.
What about the owner of the car? He still needs to have his window replaced, which isn't cheap. You, as the parent, are legally responsible, because you let your kid play unsupervised and caused an accident. Probably the owner's comprehensive insurance will pay for the window, minus the deductible, which could be considerable. Many carry deductibles of $500, $1000 or more. You should man up and take responsibility for the neighbor's expenses. Then, get copies of the actual bill, and the insurance settlement, and what is left over. Let your son see those statements, and realize what a broken car window actually costs, not to mention the inconvenience of not being able to drive to work, etc, until the window is repaired.
IMO, we coddle kids way too much in this society. Whenever I tried to teach my kids personal responsibility, seemed someone was always taking up for them, saying oh, that's ok, he didn't mean it, or he's just a kid, etc, etc. Then, my words had no meaning
I've had people actually "reward" the bad behavior, by praising them for apologizing, give them a cookie, etc. Next day, they would be doing the same destructive behavior again, and if I said anything, they would say, oh, its ok, Mr.Wilson doesn't mind! so then, I was the wicked witch, not letting the little dears do as they pleased!
No, the "injured party" doesn't need to go on a tirade about the destruction, but do let them know the actual damage, in terms of money, inconvenience, etc., don't sugar-coat it for their "little feelings". That's how we have kids turn into little terrors who do as they please.
I realize the child in this thread is 9-years old, do have the punishment fit the crime and the age. I would have him add up all the expenses, then, how many hours working at min wage would it take to pay off ALL the expenses? Then, I would have him give the neighbor his $10, and perhaps do work for him, such as yard work, wash car, etc, until at least a percentage of the damages were paid off, assuming min wage.
Oh, well, I assume I will get the usual gang of MaryLeeII bashers who will pull up old posts to show what a lousey parent I am, but just pretend my advice came from another poster!