There's a difference.
Clifford The Big Red Dog is a children's book, for children and only for children.
Harry Potter is a book largely aimed at children, but with massive and widespread appeal that people of all ages can enjoy.
Pokemon, Mario, and all the other "kiddy Nintendo games" have colossal mainstream appeal. To imply that they are somehow lower quality or that there's something wrong with liking them just because a kids can play it is a pretty arrogant and condescending mindset.
I don't know why modern gamers act like this is some secret club, where only the hardest of the hardcore can be considered true gamers and everything has to be like a movie for it to be good. Everyone tries to deal in black and white. It's a testament to a studio that they can make something accessible enough for kids to play but also fulfilling to older audiences, it doesn't devalue the game nor elevate you for having "mature" or "sophisticated" (or whatever condescending buzzword you want to use) taste.