Just a quick thought since I got in trouble for this at your son's age. Are you sure he can breathe with his mouth closed? I couldn't until my parents got my allergies tested and treated. I really wanted to please them (always was a parent-pleaser), but I didn't know how to choose between breathing and eating. It took me a little while to figure out what to do even after my allergies cleared up because it was a habit by then. But then my mother gave me a small mirror to use at the table (the kind with a stand so I didn't have to hold it). Once I could see what I was doing, I could figure out what I needed to do.