Yeah I've heard about that. Theres like an age limit to where as long as the kids are under (I think) 14 then they literally can get away with murder cuz it's against the law to convict a minor. There are literal gangs of kids who go out and do all sorts of crimes cuz they know very well nothing will be done to them as long as they're under 14. There are some really horrific stories out there of what these children are doing. Even when they get past 14 I think they still commit a lot of crimes because while they're still minors, if they do anything they usually just get thrown into a juvie of sorts for a few months, so some don't find it a big deal and continue to do horrendous things.
Because of some messed up shit that's happened I think they're working on lifting that whole law, but I could be wrong.

I know it's only fiction, but does an elementary school bullying really like that? Does they really not care whether they will be a murderer on the young age?