HELP! No elbow bend

My son has a mechanic problem in the way he throws. He is 10 and I have not been able to change this and now it is starting to effect is performance. He is stepping up to Majors for fallball and the distance he need to throw has grown. :frowning:

When he barely bends his elbow as he throws. No whip action. Its almost like he is throwing a grenade. In the AA and AAA division he was strong enough to compensate but now it is more apparent. :frowning:

He is a very good fielder and hitter.
Any help and suggestion is appreciated.

MAybe you could put some video up?