I think a lot of the distinction comes from whether you're referring more to the audience or the character of the games themselves. Of crouse, Nintendo still has the highest numbers in BOTH those categories, though as many have sort of alluded to, I don't think the gap between kids to adults on Ninty vs PS4/Xbox platforms is as large as many believe.
I've certainly heard from several adults that own Nintendo platforms (myself included), as many want to revisit their youth and still enjoy their games, and let's face it - many (especially in the 30+ range) are probably well beyond the point in caring about looking "cool". And the reverse is likely also true - of a decent number of kids owning Xbox and PS4 for just that reason (not saying it's the only one of course but likely a factor). Hell almost half the people I play with on Overwatch Xbox seem to be kids..
But yeah, if we're talking the content itself, then obviously Nintendo has far and away more "childlike" and kiddie themed games - though that doesn't mean they can't also be enjoyed by adults. And Nintendo platforms still get a lot of the more "mature" titles, especially these days, so I'm not sure why those seem to get canceled out in the minds of many when there's no shortage of them either.
"We hold these truths to be self-evident - all men and women created by the, go-you know.. you know the thing!" - Joe Biden
