Please help - I was called into the headmaster's office today because DS2 aged 6 put his hand down the back of a younger girl's trousers on the school bus on Friday, touching her bottom. He did it two or three times, despite the fact that she made it clear she didn't want him to. She told her parents when she got home and they (obviously) contacted the school. The headmaster talked to DS2 earlier today, and we also talked to him together when I was there - he was clearly terrified by this point. I have talked to him at home and reiterated that it is very serious and that you must not touch anyone on their privates.
The school have contacted the local authority in charge of families on this, as they say that it is "atypical" behaviour for a 6 year old (we are not the in the UK so not sure what the equivalent is). They may or may not call me (I got the impression that if they have had any other reports - God, hope not - they will call, but if not, probably not). The school have also arranged for DS2 to talk to a social worker a couple of times - she was at the meeting as well - to go through again what is acceptable and what isn't etc.
I don't understand at all why he did it, and most of all why he did it again when he knew she didn't want to. The video footage (which they apparently always have on the school buses) apparently shows him "all over her".
I have also asked him to tell me honestly if anyone has ever done anything like this to him, and he said no.
Obviously I'm a bit freaked out, esp the part that it is atypical at this age. What else do you think I can do? He already knew about privates being private etc so I am at a bit of a loss. I certainly don't want to trivialise it but don't want to go over the top either. Any advice would be gratefully received.