I think best thing to do is not make your kid aware of it and that there is anything abnormal about his speech. Give them time to speak and never finish their sentences for them. If they start to develop a complex about it they will start avoiding speaking as much as possible. This starts a really vicious circle where they develop more fear and anxiety about speaking which in turn can make their stuttering a lot more severe. A lot of kids stutter when starting a talk but grow out of it.