That's not to say you can't have litigation with younger kids on sexual harassment. I wouldn't say that a one-time statement is equivalent to sexual harassment. They did this outside of school, in school, on the way to school. Other kids heard it and saw it. It became disruptive.
Sexual harassment erodes the notion that school is a safe place to be.
School safety is more than metal detectors and see-through backpacks and getting rid of lockers. Sexual harassment has to be seen within this context of school safety, because there are sexual assaults in schools. There are rapes. Some kids are afraid to go to school because of sexual harassment. Yes, even with little pranks.