While you have liability only, it would still be pertinent to contact your insurance to see if there's anything they can consult you with, they may possibly assist you in getting in touch with the parent's home insurance party.
Otherwise, as others stated, contact an attorney. When you say you might have a broken arm, did you go to the hospital? You may also want to consider if you are injured, the possibility for being out of work for x amount of time that would prohibit you from actually seeking/performing work and there is restitution behind that.