T.P.
I'm a pediatric physical therapist and have known many kids like your son. Sometimes kids will even eat something like rice pudding and spit out the rice! It's often not so much underdeveloped muscles as it is hypersensitivity in his mouth. One thing that might help is to go buy a Nuk brush. Most drugstores have them in the baby aisle. It looks like a toothbrush with hard bumps on one end instead of bristles. You can work with this in his mouth, letting him chomp on it and sort of brushing in his mouth to help reduce the sensitivity. There are some pediatric therapists (usually speech or occupational therapists) who specialize or are extra good at swallowing issues. They would be able to help you more and you might really benefit from a visit or two with them. Good luck!