Upset and unsure

My 10 year old came home off the bus telling me she got punched in the face by a younger boy on the bus. After going to the hospital, I found out she has a concussion.

The principal spoke with him and the boy was taken from the movie field trip.

I keep getting told to file a police report etc..

I don't know what to do. The boy was younger. Do I really need to involve the police? I am very pissed it happened at all, but is the action the school took enough? She is missing 4 days of school.