my 12 year old front leg is bent to much before he releases the ball,anything for this
Video would certainly help. Can you post some? I also think that for a lot of kids, general strength plays a pretty significant role in mechanics at the youth level. Exercises like body weight squats and lunges and step-ups can go a long way at helping a kid develop the necessary strength to perform the pitching motion well. And these exercises can help to set the base from which future strength will be built, when he advances.
How much is “bent too much”? Less than 90 degrees behind the knee?