i don't think you should bite him back. I used to get SOOOOOOOOO mad at my sister I used to bite her but I was probably 8 or 10 or so. My older cousin bit her siblings which is where I got the idea. He is probably frustrated and doesn't know how to handle his feelings. He is old enough now to understand that he hurts others when he bites...try talking to him. Tell the other parents you are sorry and you are trying to get him to stop. Maybe the school teachers have some ideas. I'm sure they've dealt with this problem with other kids in the past. Good luck.