I've only just seen this thread Jackie.
Firsly, I'm so sorry this has happened to your son

the injuries look awful and it's clear he was being attacked and defended himself the best he could, attack comes "naturally" to an agressive out of control child, self defence comes naturally to any normal child.
I don't think you have a conflict of interests, I think you are a parent first and regardless of your position in the school if you keep a professional attitude towards your child (which it sounds like you do) whilst at work, other staff, including the Head Teacher should do so to, the Head duty of care is to protect the children.
This happened to my DD last year in year one and the child's older sibling actually came running down the playground to pull her own sister off my DD along with some other children, this also happened around the corner, slightly out of sight. When I was first told I asked if my DD retaliated and I was told that they didn't know for sure but they didn't think so (it wasn't important to the teachers and Head, my DD had been pinned to the ground for an insignificant reason and that was all they were interested in). The "other child" was made to apologise face to face and by drawing a picture saying sorry to my DD as well as being punished by losing her "golden time" in class for the rest of the week.
I was happy with the punishment given, I would have been livid if my DD had been equally punished.

to you Jackie, it must be hard, especially with DH away.
I must say I have previously taken issue (due to equal ops) knowing that my Head has an unofficial policy not to employ parents in the small school that my DD attends. I'm sure now it's because of incidents like this so that *she* doesn't feel awkward when punishing children. Your head may feel the he/she has to punish your son so that it doesn't look like your child is getting special treatment due to you being a member of staff - if that makes sense
