Certainly seek therapy for him but be careful not to fret quite yet. The brain is going bonkers in kids at that age. It could be a form of transitive tic that will air itself out. Regardless he will benefit from therapy I’d reckon. Whatever you do, if it is indeed a stutter, allow your home to be a place of peace for him. Patience, grace, and accessibility. Don’t finish his sentences, don’t look at him with pity or frustration if he’s trying to say something.