The irony is that teenagers (so still children) are far more interested in mature games like FPS because they seem more adult. I am 37 years old and have been gaming for 30 of those years and although some violent games are some of my favourites FPS have lately been boring the shit out of me.
I mean, just how many times can you shoot something before being sick of it?
A "kiddie" game like Mario paradoxically has more depth than it's cartoon graphics would have you think and therefore appeal to adults as much, if not more than kids......

GameCube/GBA era had the whole "who are you?" campaign that seemed to be targeted at a late teen/young adult audience.

unless you're including that demographic in "children".

but i can't think of any non-children marketing from Wii onwards. 

Yep. Too bad some believes grey and brown makes this mature.

Nintendo points itself towards people who want to have fun and not look at blood and guts and guns and tits and death and brown and grey.

So, basically -- children! 

And to be serious, I find it very narrow-minded when people, in this instance Nintendo defenders, equate mature content with killing and nudity. But once they dare look outside their closeminded world of vivid cartoon characters, theey might discover other interesting ideas. 

Oh, and sorry, but if you are an adult and don't like nudity, something is not right...

I study color theory at school and marketing schemes. Nintendo is primarily and foundationally aimed at children and families. I studied color theory for what attracts children women and males and people in between. Nintendo consoles are for everyone but are  marketed to children and families. 

Thats the truth. I almost gave up on playing their games on consoles all together, but it didn't stop me from having fun once I got over half of the console glitches. Skyrim and Fallout were masterpieces.

When you make the statement including the words family friendly and a Nintendo fan replies to that statement saying why is Nintendo just for kids like that's what you even said, you know even Nintendo fans themselves think it's a children's system.

QFT. And even when I was a FPS fan, I preferred Duke Nukem 3D, with its easy-going, humourously over-the-top and parodic style to Quake II, that despite being excellent and pioneering in many things, took itself so seriously to paradoxically become less believable than the Duke.
About Ninty, as I already wrote, I think it's more perception rather than reality: its systems are perfectly capable of any kind of games, and since Ninty ceased strongly censoring third parties too, they have adult ones too, but its image is kiddy because its marketing is and most of its biggest games and franchises either are very children-friendly or they have kiddy graphics even if they are targeted also at adults. This wouldn't be a problem it wasn't overwhelming. Adult people not unsecure can perfectly accept that part of their game libraries most important games have funny cartoony graphics, but if they are the vast majority even people self-confident enough could start feeling not totally at their ease, or even if they still are, they could feel they aren't the intended target of that system.

skyrim even on an older pc with just some mods and fixes is just so much better.

the shroomkingdom mod is sooo great...