Kids are the main audience of the series but not the sole one. It's not that much different from other properties like Kingdom Hearts, Digimon, Transformers, Harry Potter, Yugioh, Star Wars, Dragon Ball, Marvel & DC etc. Part of the reason why those franchises became as big as they did is because they appealed to so many different demographics. Paying customers are allowed to complain if they find certain aspects lacking. Even children have certain dislikes and don't blindly love everything about the entertainment they enjoy. They're just not as vocal as adults due to various reasons.
That's not always the case though. Take Tokyo Mirage Sessions for an example. It was clearly only ever going to appeal to a very small audience, but it released for $60 and bombed. They ported it to the Switch four years later for the exact same price and it bombed again. Consumers didn't tell them it was worth full price, Nintendo/Atlus felt it was worth that much. It's not that unusual to see series with limited appeal released for the same price as bestselling series such as Pokémon, Halo or Call of Duty.
Or just look at the Wii U and PS Vita in general. Despite the small install base, several games were still being released at or near full price. And some of the games that sold poorly rarely went or sale or never received permanent price cuts. Even look at certain top-quality PS4 games that retailed for $40 upon release such Ratchet & Clank 2016, Uncharted Lost Legacy, Crash Bandicoot N Sane Trilogy, etc. They could have probably been priced at $60 and still made a profit but the developers thought the length of the games didn't justify it.
I think certain indie studios are more likely to price their games according to the market. But when it comes to large and mid-sized developers and publishers, their perception of what the game is worth is often the main factor in determining price.