Tai chi trains and refines natural movement, which on the surface may seem like a paradox. Why would natural movement need to be trained? In actuality, natural movement gets covered up by unnatural habits, which have to be untrained in order to allow natural movement to emerge and flourish.
Kids already know how to move naturally, so trying to teach them tai chi has little effect in this regard. People usually don’t seek out things like tai chi and yoga until they realize that they have lost their natural movement and want to get it back.
However, teaching kids how to consciously move naturally can help prevent bad habits from forming, and improve their coordination beyond what it would otherwise be. Furthermore, there are few things more powerful than a practice that is continued for a lifetime, so imparting an appreciation of their natural movement and full range of motion, as well as the discipline required to maintain them, is one of the most valuable gifts that a child can be given.