The fact that the age of the girl isn't disclosed makes it a bit tricky to comment. Although from reading the report i understood that the kicks didn't really hurt him (by his own admission) and after only a week they were friends again. I am also, perhaps falsely assuming an adult is usually present? I wouldn't want to leave the two of them alone if they were my kids. If all these facts are true then it seems unnecessary to involve a court of law.
However, i have had little fights growing up with my own brothers, but i tell you what... never would they punch me in the face! provoked or not! It seems a very extreme response to a few kicks 'that didn't hurt' though, doesn't it? Also, i think courts or police sometimes act just to put other people off doing same. As a deterrent if you like. I can see that as beneficial to some kids, say if there parents are always out or just don't give a fuck, it might prevent some poor kid somewhere from getting a good hiding from a sibling.
Just looking at the facts presented though, i would say it was a waste of resources and should have been handled by the parents. Unless there is something we don't know. ?