Shavuot: Accepting the Torah Class 16

[Edith1]

I hope this posting is not a duplicate.  I posted a response on Class 16 but I don't see it in the posting board.
What I said was that I don't understand why parents and children are not liable when damage is done by children if it is the first time.  If a child were to damage something in a shop wouldn't the parents be liable to pay for the damage?  Why then would they not be liable if school property is damaged?