80% of children who stutter outgrow it. So 'worrying' is not necessary because the chance of outgrowing is 80%. I would suggest the following guidelines: don't pay attention to stuttering (for spontaneous recovery), reinforce automatic natural speech but don't let stuttering bother him and don't try to 'intervene' like controlling, preparing or other techniques. It is counter-productive to pay attention to stuttering, see this [PDF document](https://drive.google.com/file/d/1d8xZ4xb1DuZ__lmIWyT-oXQaJlArA8_K/view?usp=sharing) that explains how paying attention to stuttering escalates.