I don't have any investment in playing as a child character - but I'd like to see more child NPCs around. Children were all over the place in the towns in FFXI, but you can count the total number of children shown in this game in one hand, most of them featured only in cutscenes. It makes the so-called city-states of Gridania, Ul'dah, and Limsa seem a bit unnatural - if these are really cities, where are the kids?

On the topic of Padjal, though, SE has plenty of lore-safe reasons they could choose to add them as a race if they wanted to, based largely on the fact that no one really knows for sure WHAT the elementals are thinking or their motivations are. The elementals could one day decide, for whatever hidden reasons (or even unhidden: it could be done as a reaction to the Calamaty, for example, or to prepare for an upcoming disaster that the elementals sense coming before anyone else), that they need to pop a crapton of Padjals and send them adventurin'. Boom! Playable.

The elementals could even choose to make people of races other than Hyur into Padjal; just because Hyur are the only ones so far chosen doesn't mean that they're the only race that CAN be chosen.