Yeah, designing games geared towards kids and younger audiences isn’t just about story/aesthetics, it’s also about difficulty. Most young kids don’t have the attention span or critical thinking skills to sit there and try to beat an enemy or puzzle that older kids or adults would find genuinely challenging.
I could split Nintendo games (I’ve played) into three groups based on target audience:
Younger: cute art style, simple challenges, short game play for young children; Kirby, Yoshi
All Ages: easy-to-learn basics to get you through the main game, but there’s more complex stuff and greater challenge if you want it; mostly pick-up-and-play but not TOO short; Mario, Pokemon, DK Country, Super Smash Bros.
Older Gamers: more (relatively) mature subject matter, challenge from the beginning, complex mechanics and/or puzzles or both to get teen/adult brains going; Metroid, Xenoblade, Fire Emblem, Zelda BotW and TotK (previous Zelda games would be in my All Ages tier)