Even if there are and were exceptions - all the 12-year-old ones who started playing WoW once, are already adults. And if you want new players to join, it's much more likely that those below 16 will not understand WoW and find it worthy the time. Modern kids prefer shooters, games with emphasize on 3D effects, etc, while spending extra time on thoroughly reading questlines, going deep into lore aspects, etc... you understand me, right? As I said - RPG is not a kids friendly genre. So dumbing the game down in order to make it more appealing for children was a fail.
I didn't find the right solution from the Internet.