I stutter. Both of my children have gone through stuttering phases. If I was you I would relax, talk slowly to my children and not draw attention to it. If my child was stuttering while excited I would encourage them to calm down a moment and think about what they want to say. I expect there is a very high chance that your kid will snap out of it. Both of my kids returned to fluency. One was after a couple of weeks. The other went up and down for about 2 months before she figured it out. If it isn’t sorted in a few weeks I would journal and record what I was seeing. If it wasn’t sorted in a couple of months I would reach out.