When playing a game of catch with your son, start off with just a simple toss back and forth - no velocity and no real effort to get the ball anywhere but to you and you back to him.
After you both feel as though the toss back and forth has your son looking straight at you, and nothing else, take it up a notch velocity wise - but not much. Watch for any sign of your son's tendency to start gazing down at the ground, any sign. With just a little more effort playing catch then you started off with, he shouldn't revert back to his old habit.
Continue your game of catch, increasing your arm strength and his to bring the ball in a little faster. Remember, build this up gradually.
At the point where the velocity gets up there, and he starts to snap his head down - STOP. This is the point where he starts to howitzer the ball without really thinking of what happens next.
Bring this to his attention and ask "what's going on here." A shrug of the shoulders and a "I don't know," is no kind of answer.
Start all over again with the gradual tossing, then start to build up velocity until he looks down again - STOP. Bring this to his attention, again, and ask "what's going on here." A shrug of the shoulders and a "I don't know," is no kind of answer.
Start all over again.
Now sooner or later two things are going to happen:
- He'll pay more attention to that point in time when he stops thinking of what he's doing, and corrects it.
- He'll walk away and tell you that this isn't fun any more, "let's quit."
I honestly don't believe there's any middle ground here - but then, I'm not privilege to coaching youngsters. On the other hand, somewhere along the line as he gets older and stronger, this is going to be a safety issue for somebody, either for himself or for a batter.