Hello vicente, For only being 11 years old, your son has nice rhythm and timing. This is what I see:
Posture and Weight Distribution is good in the beginning of his delivery .01 - .03 in the video. His posture is in an upright position with his chin over his belly button and his shoulders are in a relaxed position. His shoulders are in a direct line with home plate.
Early Momentum and Hand Break. This is where your son lacks early weight shift down the mound. You can see this at .03 - .04 in the video. When his leg and hands start to move down, your son needs to shift his front hip towards the catcher. Be careful and just don’t throw the front hip out there without an explosive movement from the back drive leg. The front hip should lead the front shoulder. To maximize explosive weight shift, your son’s entire back foot should be pushing into the ground and back against the rubber with his weight evenly distributed over the entire back foot. The foot should stay flat and in contact with the ground as long as possible.
Here is the Wall Drill I suggest doing with your son. Just make sure he does not rush his motion, rather just work on getting things started early to create momentum and promote a longer, more powerful stride. Then you can gradually accelerate down the mound and explode into ball release… This will also help him get the rest of his body in sync. Look at the image below and you can see what I mean when I compared your son to a MLB pitcher about gaining early momentum.