The first of your vid clips seems to be marked “private”; however, the others are viewable.
The clips I could watch are a reasonable start; however, I do have a technical suggestion for your future video work.
In addition to taking video of your son from 3rd base, I suggest (strongly) that you buy a cheap (~$30) tripod for your video cam and use it. One of the biggest mistakes I see (and it is very common) is people using their hand-held $400 camcorder to make shaky, jumpy video of an athlete in motion whom they later want to analyze for subtle mechanical issues. It is a basic axiom of video analysis that you cannot really look closely at your subject’s movements when the video field itself is moving and shaking.
All that being said, I didn’t see any red flags in your son’s mechanics. The strikes he threw looked filthy and his sidearm mechanics and release will confound many hitters.
He obviously needs to develop a consistent release point, but the way a pitcher does that is by developing consistent, repeatable mechanics leading up to the release point.
Every practice session when you are working together on pitching, you should make sure that he is setting up with the same balanced posture and from the same place on the rubber that he is comfortable with. His leg lift should always be the same and he should be getting his front hip moving toward the target before he reaches the top of his leg lift. His posture should be maintained through to foot-strike without too much up-and-down movement of his head (and without left-and-right movement of his head, either). His head and his eyes should track straight to the target (remember, we are essentially a predatory species–our eyes are on the front of our head for a reason and they efficiently guide our motor responses to hit or attack what we are looking at).
House taught my son to start every bullpen session the same way and to make sure that he doesn’t jump ahead of himself to work on something out of sequence. Every bullpen starts by re-establishing the optimum balanced starting posture, getting the booty going toward HP at the same time that leg lift commences, etc, etc, etc–optimizing first-things-first and working toward consistency and repeatability of mechanics leading up to the release point is probably all that your son needs to do, too.
One final note, for now–I thought I noticed that when your boy threw a pitch that he didn’t like very much he sort of “windmilled” his arm afterward, and maybe showed his disappointment. This is something to correct in practices, so that he will not carry it into games.
Undoubtedly, given some of your earlier discussion, he has been treated to far too much foolish criticism from coaches during games whenever he throws a bad pitch–I see this a lot: Kid loses control in a game, coach starts shouting all sorts of useless mechanics advice toward the mound, very naturally the kid cannot make use of this advice under game pressure, so the kid becomes a nervous wreck and starts showing nervous or defeated body language. Opposing hitters love to see that, of course, but it always breaks my heart. A pitcher who shows no emotion and no defeated body language when things are going wrong is perceived by the opposition as being in control, even if the pitcher doesn’t feel that way deep inside. It is an outer attitude that can be cultivated–but you’ve got to decide to do it, and you’ve got to practice it just like mechanics.