Dear Sammy.
You don't worry.I will help you.
You should report the case to teacher .because the F.1 boy must tell the case to teacher .If your friends to confess the case,may be can lower they punishment.
Tell your friends that hit somebody and lock people in the toilet is crime.If the F.1 boy take legal action,your friends have more trouble.
You should to comfort your friends,because your friends is unhappy.AND you should advise yourfriends apologized to the F.1 boy,becaue is your friends put a foot wrong.
I hope my advice can help you.I express your friends can out of the wood.
Chris