Your child may be going through a developmental phase, as many children do. Or, he may be developing a true stuttering problem. Seek professional help NOW. Contact your local public school's speech-language pathologist(SLP), even if your child does not attend that school. A knowledgeable speech language pathologist will be able to diagnose which is the case. If it seems to be just a phase, the SLP will probably recommend a few follow up evaluations to make sure. If it is a true stuttering problem, the sooner your son gets help, the better. The right treatment at an early age may help prevent a stuttering problem from worsening, or becoming chronic and life-long. Whatever you do, do NOT follow the old, outdated, and very harmful advice, "just ignore it and it will probably go away". Contact the National Stuttering Association for more info and advice. Good luck.