Just about every shooter that I can recall had warning signals that those around them should have addressed. Parents or relatives chose to ignore them or didn't know what to do about it. I don't recall reading about a sweetheart of a kid one day just snapping, there were always signs.
As far as the guns and kids, I feel you are doing your kid a disservice if you leave them alone with no way to protect themselves, that is of course after you have shown them how to use a weapon.
Couldn't agree with you more on the pit bull thing.