I liked it better when the charas were in their 20's and up with a couple of random kids in between.
I think that's one reason there are less kids, because the age range is already in the teens. If you look at the final fantasy's that did have kid charas, most the main charas were 20 or up. Plus, most people believe that if the game is in a general age range of the players, that the players will like it better. I think FFVII was the last one with the charas around their 20's if not already in them. Like in FFVII the "young" one was Yuffie, who was like what 16?
In newer games the main charas 16, and they prolly wouldn't want the game based around kids who are between like.. 10 and 16.