I’m an SLP and my own 2 year old started stuttering recently (which is pretty common around this age). There is a lot of cognitive and skills based development happening around the 2-3 age range, which is one reason why there is typically an onset of stuttering around that time (higher cognitive and motor demands but lass capacity to perform them). Direct therapy is best when a child is showing signs of discomfort, struggle, excessive tension, or frustration while stuttering, but they also should have the cognitive ability and self awareness to apply and practice some of the strategies they learn. Indirect therapy may be more appropriate at this time. This is where you support the child who stutters without directly addressing the stuttering. Things like - modeling easy relaxed speech, maintaining eye contact and a neutral expression while the child is stuttering, letting him express his thoughts without finishing his speech for him, showing excitement and interest in what he is saying, reducing time pressure to talk quickly, encouraging turn taking so everyone in the house gives time to everyone else to speak without interrupting. You can also play voice games with your nephew where you take turns changing your voice (quiet vs. loud, fast vs. slow). This is an indirect way of showing how we can change our voices to help manage our speech. This is a building block of later direct therapy where you can practice fluency strategies or stuttering modification to stutter more easily. If you have any doubts or concerns, you can encourage contacting an SLP that knows about stuttering and get an evaluation (evaluation doesn’t always mean you have to start doing therapy). Stuttering is speech diversity and, like someone else responded, it’s just a different way of speaking. One of the best ways to help right now is to show your nephew that you are interested in hearing what they have to say, no matter how they say it.