Im not saying adults can't/don't/shouldn't play Nintendo games.
I'm saying that regardless of WHO plays them, their designs are objectively designed to attract children.
Super colourful/high contrast, round shapes, minimal realism, simplistic character designs, clear non-cluttered UI, playful sound design, low-danger enemies (goofy, smiling enemies in many games),
Nintendo almost never uses muted palettes for their flagship titles. Always lots of yellow, red, blue, green.
Their entire design language is catered to kids. Theres no way around this.
Adults can still enjoy them. But they are catered to children first. Miyamoto himself would admit this
Just like COD. Catered to adults. But kids still play and enjoy in large numbers.