Stutterers generally hate hearing other people stutter because it reminds them what they actually sound like. He’s probably too young right now, but The King’s Speech is an excellent movie to show as it captures what it feels like to stutter and just how daunting of a task it feels like to speak, along with the pride you feel for the character when he succeeds. You could also point out some famous stutterers (Joe Biden, James Earl Jones, Ed Sheeran, Samuel L. Jackson, Bruce Willis).