First advice is to not freak out and start being all worried about his speech. Kids can pick up on that and that usually contributes to negative feelings more than anything. Secondly, I haven't heard of any actual evidence linking psychological trauma to stuttering. People often make this connection but I don't know think there's any proof behind it. If there were, we'd see a lot more stutterers out there. Stuttering often has a genetic component. Environment has exacerbate stuttering but it shouldn't be able to cause it on it's own. Listen patiently, give your kid space to speak. Go see a speech pathologist experienced in stuttering, not just any speech pathologist.