What does the HT say? Isn't this something that should be followed up by the school? I thought that this would be a child safety issue. Possibly social services but that would be the HT's decision, I guess. Have you passed on your worries to the HT? Personally, I would not do anything on a 'personal' level. I think this should go through official channels and the HT should be taking it further. However, not being a member of the SLT, hopefully someone with more experience will be able to give advice. I know how worrying this can be.