1) You can most likely sue the family of the child which bit him; of course, this is only worth doing if you incurred significant medical costs, or you son will have some disability, scarring, etc. from the bite.2) If the school knew that this child was a biter, was violent, had threatened your son specifically, etc. before, you could possibly sue the school for negligent supervision. As above, it's only worthwhile if there are enough damages, costs, or injuries to justify a lawsuit.