MJ, please don't get me wrong. When I refer to gaining arm strength, I am not expecting a 10 or 12 year old to start a strength program. I am talking about more throwing. The best way to strengthen the arm is to throw. I can appreciate what you do as a coach, as I have also worked with pitchers at the college level for 17 years. As for flaws in this delivery, from these photos, there is no way we can pick apart his throwing motion. He lands with with a good, strong position with his front foot, his arm pronates correctly when he releases. I can not see what it looks like when it comes out of the glove, nor when his foot lands to throw, but the mechanics of how his arm works are fine after release. As I said earlier, level out the head and shoulders, and you will have a motion that is proper.
I have a feeling the thumb may be in front of the ball when he gets ready to throw it, instead of underneath, and that is why the head is being pulled off to the side like it does. Also, he may be being told to get his arm up more than his body is capable of. If the elbow is level with the shoulder, and parallel to the ground, he will stay healthy for a long time. Not every pitcher throws "over the top". Look at Randy Johnson, Jake Peavy, and plenty more. The arm just works better from the side.
If you ever want to see if his arm is working properly, put a football in his hand. If he can throw a spiral, his arm works fine. Fix the head and shoulders and he is good to go.