True to a certain extent, I'd say they're more aimed at families than just children. Though even then, a game doesn't need to be rated M or 18+ to be aimed at adults. Games can be mature for reasons other than the gore or swearing that could get a game a rating like that. Like No Man's Sky is rated 7+ but I wouldn't call it a kids game.
Not that Wii U has any games aimed at adults without an M rating outside of maybe Monster Hunter, but still an age rating shouldn't be the defining factor for if a game is mature or not. Though I also don't see a problem with making games aimed at children when there is a lack of good games suitable for kids that aren't made by Nintendo these days anyway, not counting F2P mobile games.