As a lifelong stutterer (now 39), being able to calm myself and lower my stress has done more good than all the therapy I went through as a child and teen. Practice yoga with your child, or calm breathing techniques, even meditation. It doesn’t have to be framed in being related to a stutter, maybe you yourself are into or could get into a form of relaxation and then involve your child. Once they learn some self-calming techniques, they can incorporate those techniques into lowering their stress associated with being teased, not being able to verbally express themselves as they would like to, etc. As a parent, my heart goes out to you and wish you the best!