Children benefit greatly from staying flexible, not only does it help with martial arts but also every other sport. The reason martial arts is one of the best activity’s you can do for stretching and maintaining a supple body is the fact that most of the skills for martial arts require you to be reasonably flexible.
Being flexible makes you more coordinated, a bigger range of motion in the joints, better stamina, less tension in the body and mind plus it sets a healthy habit for full active adult life.
Its a well documented fact that flexibility leads to a more active happy life for all your life.