My kid started to show signs of stuttering at the same exact age. It got worse when his idiot grandmother started laughing at him when he would stutter. After she went back to Korea, I had a talk with him about how it’s horrible to laugh at people and it wasn’t his fault, and then we as a household just decided to ignore it every single time he stuttered. He got over it after a few months. And developed a “don’t give a fuk” attitude about just about everything. Just be supportive, and act like it’s not happening.