how many kids were there?
and how can "one" witness pick your kid out of the group?
unless they hauled him in to the police themselves or the cleaner made a citezens arrest or the like?

stick to the "everyone says our son broke the window so we figured that he had and arranged for the replacement to be fitted. this was before the former owner (who we worte to) decided not to show up everytime we had agreed to have oseone come out to fit the replacement (at our cost you understand)
now that you have been jerking us about even more we have asked our son and he says there were a few of them throwing items about that particular afternoon and, after consultation, you cannot proove it was our son (we don't need to proove it was, innocent until prooven guilty and all that malarky) as he is only little and, faced with getting a bollocking from ourselves foolishly admited to the crime, unaware of the repercussions of his statement. there was no formal complaint made to the police upon which they would have questioned our son in our preseance along wih the other lads who were at the scene so your "witness" is uncoroborated and nothing has been done by the book.
you can whistle for your money for the window"

or words to that effect

of course, if the police HAVE been involed, which i don't think is the case by what you have said, they would have done things "by the book" and this is clearly not the case
you have bent over backwards in an attempt to rectify a situation that you have assumed your son got himself into without getting "official" about it and this has clearly failed so the greviance has to be taken up with the orignal seller of the property

the right thing to do would have been to have the windows and doors boarded up while it was unoccupied as most insruance companies require the premises to be occuped during the day