2 year old starts stuttering?

2 year old starts stuttering? I babysit a two year old regularly who keeps on stuttering when he starts a sentence with „I“. His parents also noticed and are getting worried. Do you think he is developing a stutter or is it just a quirk? He speaks well for his age and has no problem constructing longer sentences (8-10 words). It’s really only when he refers to himself as „I“ that he starts stuttering.