people with bad intentions entering schools is certainly common. That's why schools have locked doors.
A couple of points.
1.Filing a lawsuit isn't winning a lawsuit.
2. lawsuits serve purposes other than compensation for victims. They are an orderly process for looking at an incident in as unbiased a way as society has come up with, to identify problems, people who make mistakes, or don't, or people or systems that are or aren't culpable.
3. It is outrageous to ignore the effect this incident had on the children and people who didn't die, probably only because the police responded quickly.
Do you all really have no sympathy for a young child who will live the rest of their life knowing there was a person who in all likelihood wanted to kill them ?