Adult/Parent Loitering around my childs playground!?

My child was thrown to the floor and kicked in the head whilst at school when he was 10.I went to the school and first expressed my concern at how a teacher had split this up,but i had to hear of the incident from my child.I told the school that i would not put up with this.I told them to tell the other childs parents that if he ever strook my child again i would call the police.I don't know where i would have stood legally had i have to of persued it but i do know that it never happened again,hopefully the parents got the message that they are responsible for their childs actions.