If the kid didn't listen to him he should have arrested him.
I actually think that is a law, non-compliance or something like that. Too much Tort Law and International Criminal Law has crowded out a lot of the domestic laws. However, he did not arrest the kid, he assaulted the kid. The assault is the issue.
The issue isn't that the kid is a smart ***, or a jerk, or whatever you want to call it. The issue is that an adult, a police officer none the less, body slammed a child after choking him. If that isn't use of unnecessary force than I don't know what is.
If he was arresting the kid and the kid socked him in the nose I would say the officer did nothing wrong. However, as far as I could tell from the video the kids were of no threat to the officer and the officer was simply trying to question them, if you wanted to put it like that but lecture fits the bill better. The kids weren't read their rights, the kids weren't going to be arrested (most likely), they were just getting a lecture from Super Cop. So his physical actions are no different than if joe smo came up and choked and used force against them.
What is especially disturbing is the officers face. That man SERIOUSLY needs some anger management and should be carrying a weapon of any type. He could have just of easily took his gun out and shot the kids. Now wouldn't that have made for a hell of a headline?!?!?!?