To answer your question, if an LEO saw the 11YO point a gun @ someone, and if that 11 YO didn't follow commands or they felt another life was in danger, then the correct response is to neutralize the threat.
As far as the gun in the back seat, how can you remove the cartridge and there still be a round in the chamber, if that is what the news said, then that is part of the problem.
A week or so ago, a county south of me, a 17YO "teenager" decided to hold up a gas station with a gun (BB gun), most unfortunate for him, the owner came out of the back room with a shotgun and shot him dead, no charges filed, the BB gun looked like a real gun.
Had it had been real, and he pulled off the robbery, instead of leaving, sometimes they decide to leave no witness's, saw that at a pawn shop in town earlier this year.
We can debate this forever and never get anywhere. There are a lot of guns in the U.S., banning them won't fix anything, I think a mandatory gun owner IQ test is in order, and start making people responsible for their own actions would be a good start. And instead of releasing people committing crimes, how about actually making the stay miserable, i.e. chain gangs, breaking rocks, etc.....