I have. When I was 7 years old I was hit by a car and landed face down. I was knocked unconscious and in a coma for ~ 2 days. My stutter developed after my car accident. My mom explained to me that hitting my frontal lobe (Broca’s area, the part of your brain where speech is located) is what caused my stutter, since I never stuttered before age 7, and I was also a little kid who would never shut up. I wonder if your son hit his head and never told you about it? Feel free to message me or ask any questions