Looking much better than the first video. Hand separation is good. Front side is not overly elevated like before.
He is rushing his throwing hand (most kids do). Slowing that down usually comes with age. Right at foot plant we would like his throwing hand to be coming up and just about shoulder height. If you stop video with his foot about 4-6 inches from plant you can see his throwing hand is already bent and above his head. We want the front and rear side to move with the same speed. Again, MOST kids throw this way and it will take a while for you to slow down his throwing arm motion during his separation.
Another problem I still see is that his throwing arm is straight in the air, like a catapult, before his hand ever gets even with his shoulder. Because of that he has a ton of leaning in his upper body to the left side, which is not good.
Here is the next thing:
The way he finishes with his drive leg looks very unnatural. See how bent over his upper body is. His drive leg come straight forward and not really around him as it should if he finished forward and down. It looks as if he is purposely lifting his drive leg as though he has to get over a hurdle. I would keep him from doing that and let him just move his drive leg more naturally in motion around his body. Just look very strange to me.
Hope that helps.
You really need to get him to drive forward with his body and arm and not up and around. I think the catapulting of his throwing arm up and way over his head is the cause of much of the problem. Fix that before you work on almost anything else, in my opinion.
Here are some stop action shots of a kid I work with and of major MLB names in the same position I have stopped the video of your son in the first image above. Big difference.
10 Year old kid I work with:
See how none of these have their throwing arm straight and already extended before their throwing hand get in front of their shoulder.
Keep working!!!! Most important thing... IS HE HAVING FUN????