Yes, I know, sometimes there is nothing they could have done. Truly. But most of the time, the parents completely ignore all these warning signs because "not my darling child, they're perfect."
Parenting is the only job we have in this country where we applaud effort vs the result. I know it's hard (I'll even concede it's one of the hardest jobs in the world -- that's why I opted out), but if you want to have a child, people need to understand what that all involves.
Charging parents is the only way to get the people responsible for the child to take the behavior of the child seriously. If they know they can be held accountable, maybe the parent thinks twice before gifting a gun or leaving them easy access for a kid to get.
It's a start, a sad one, but it's really the only hope I see in my lifetime. But I'm in WI and hunting and gun culture is huge here, maybe other places are more sane. I don't even think we could get a law passed to require you to have insurance if you have a school-aged child in your home and own a gun. Which is insane, can't drive a car w/o insurance...