My wife and I were talking about this topic after seeing BDO's trailer about Shai. We both thought it would be cool to play a younger character (teenager) going out into the world. It certainly is a popular theme in manga and anime.

Yet, it wouldn't work here. Perhaps, it could have worked if introduced in ARR. That way S.E. could have developed the game with that concept in mind. But, that ship has sailed and we are not going to see playable children for reasons already gone through in this thread.