Pitcher might need a quick mental break to just ease the tension a bit. It may not work at all, but maybe tell a joke or point out a hottie or something like that. If he's struggling, he's most likely already thinking about every little piece of advice he's ever gotten.
Trust me, your son's pitching advice isn't going to help much. Besides, what are the chances that your son (or any catcher at that age, really) truly knows enough about pitching to spot flaws and make the proper suggestion for adjustment. Maybe I'm wrong and he's know pitching mechanics inside and out. Or maybe he knows what Bob Gibson thought Tim McCarver knew ("Get back behind the plate...all you know about pitching is that you can't hit it").