Children still enjoy the fuck out of Nintendo stuff. As much as the Aimiibo crap is bought by strange unwashed man and women children with that same damn green Zelda shirt(which annoys me as I like wearing my green Phoenix shirt). In my experince managing my Target's electronic section kids still love Nintendo games. Kids still made their parents buy Splatoon, Mario Maker, Smash, Kart, whatever. Kids are still playing the fuck out of the demo system. The Wii U demo system is probably the most popular one.
It's just at the end of the day it is seen as a kids toy and there are cheaper kids toys and I believe especially with multiple kid households, something like the PS4 or Xbox are more worthwhile systems. You've got a teenager or something, parents seem more interested in buying something not for children. It's for them but also the whole household. You're kids growing up, seems like it may be worthwhile not to buy such a kids device.
Nintendo may not have the lockdown on kids thanks to a great many things, but I doubt it's the neogaf nintard who makes up most of it's userbase.
What Nintendo lacks is the audience that buys consoles for NBA 2k16, Fifa, Madden, NHL, CoD, and GTA.