At that age it’s kind of normal for kids to stutter, but take this from someone that grew up going to different speech therapists. I think they worked to some degree, but it made more self-conscious about having a stutter, which was good and bad, because I’ve come to accept it, but it’s also made me set my own limits on how much I can contribute to a conversation. DEFINITELY be supportive. I was talking with my dad once and started stuttering. He thought I was making fun of him and got really mad. He started yelling “You are not broken, speak clear, blah blah.” He apologized sometime later, but it definitely severed our relationship. I would not say to ignore it. Maybe try speech therapy for sometime and see if it helps. Also, if he starts stuttering don’t correct him, because I think you’ll be just drilling more into him that stuttering is wrong, making him feel more frustrated and worse.