Not saying Nintendo isn't still family friendly. It's just that they're less insistent on being family only. Wii U era felt like they were trying to be as overly safe and sterile as possible. Switch era Nintendo is still friendly for kids, but they're not afraid to get a little dirty either. 

I wouldn't say that. Since N64 era Nintendo has tried to shed some of the 'Kiddy ' moniker they earned with varying degrees of success. The Wii U they published Bayonetta 1 and 2, even paid to have a model cosplay her in Playboy, they also tried supporting other titles like Devil's Third. It is just their opening market push was trash.

Because it focuses on being family friendly with its games and marketing. If they didn't want that stigma then they would be doing the opposite. Their web site looks like a kid store. In each rating, Nintendo has twice as many E, E10 and teen rated games each compared to M rated games. Sony has twice as many m rated and teen rated games each in comparison to E and E10 games. You see the difference in focus? The only ones who really care about that stigma is the older ninty fans. It doesn't affect any other gamer fanbase.

Nintendo is no longer kiddie because “creative” (and retro) is back in mainstream style.

A lot of people seem to be mistaking kiddie and childish with family friendly.

Do people not remember the abysmal WiiU ads? Those are long gone replaced with ads that focus more on the product and its appeal rather than 'family time'.

That has nothing to do with being kiddy though. Gamers today don't give a shit about ESRB ratings anymore. 8 year olds are playing Fortnite, a Teen rated game. While actual Teens and Young adults are also playing games like Rocket League with no shame involved. Ratings have nothing to do with marketing or perception. Switch has Marketed E rated games to young adults. It's about how you present your content, not what letter you slap on it. 

It's about the content of the games, which is tacitly what the ESRB rating represents, not the marketing.

Huh, never realized that BOTW, XC 2 and Bayo 1 and 2 were kiddy games, nor the upcomming Bayo 3 and Metroid Prime 4.

What adult or mature content do you think that BOTW has? @Nautilus

Yes, but the ESRB rating is irrelevant to the actual marketing and target audience of the game. It's like MPPA ratings, MCU movies are PG-13, yet they're aimed at kids all the time. For Video games, ARMS is E10+, yet was primarily marketed to adults. Pre-Switch Nintendo had a Kiddy image because the overly sterile aesthetics and abysmal marketing of their games featuring 10 year olds bouncing around gave them that label. Post-Switch Nintendo is seen as cool because their games now have a bit more bite (even the Mario and Zelda ones), and are able to present it's family friendliness in a way that's tasteful, and attractive to people of all ages.