Not necessarily an answer to your question, but I wanted to thank you for reaching out for help around this. When I developed my stutter (when I was not that much older than your son), my own father was harsh and cruel. He would yell at me to slow down, or 'spit it out,' or shake me. And of course, shaming someone only makes it worse. I can't speak for all people who stutter, obviously, but for me, simply being listened to and not rushed, and feeling safe to stutter when I talk, is so profoundly beneficial. I've heard it's not uncommon for kids to develop a stutter when they're young, and they might 'grow out of it' after a while. So that might be the case. But if it sticks around for a while, just listen patiently, and let him know that it's safe for him to stutter -- or not-- around you.