Not copyright, trademark. At least, that's the rules those comments assume Disney is following. It's pretty dumb, I can't think of any world those characters get genericised, but eh.

it’s that they can lose the trademark if they don’t try to defend it

So the copyright and trademark system needs to change then.

Also, those laws were essentially ghostwritten by Disney and the like, so I very much doubt that wasn't an intentional thing so they can go "look, we have to sue you, our hands are tied!"

they can lose the trademark if they don’t try to defend it

This is true, but that's if another company is using a similar logo as their own. Like, if a pet store used the Mickey Mouse logo, of course they're going to be sued.

If a daycare uses Mickey Mouse to decorate their classroom, Disney doesn't have to sue because the trademark isn't be used separate from Disney. The Daycare, and kids, are using it because it's Disney, so there is no confusion about trademark ownership.

At the very least, Disney could simply write them a letter allowing them to use depictions of Disney characters inside the school so long as it's not for advertising or commercial purposes and the art is done by a student or teacher.

I anal as well

A simple crease and desist letter surely suffice for this, right? No need to waste resource suing a daycare for copyright infringement?

U ANAL?

No really such thing as fair use in trademark but it's definitely possible to not be an asshole about it. You can definitely allow use, the question is whether you assert control over use of the mark or not.

You wouldn't want to allow extreme cases (a daycare Disney-theming itself completely associating itself, unilaterally, with all your IP and by extension looking like a Disney-licensed and associated daycare) but "as minor part of a larger artwork, or a single mural of a single character not publicly visible" avoids damage to the mark's image.

From the other POV, as a daycare, you should only ever do murals of Mickey if he's holding a giant cookie.

The standard for losing a trademark essentially boils down to "no reasonable person would expect the public to know it's a trademark, so any infringement can be assumed to be accidental". So things like dry ice, heroin, escalator, gasoline, trampoline, flip phone, and teleprompter. Common words where the fact that they were once trademarks is obscure trivia. The more commonly cited examples of genericized trademarks like Kleenex or Band-Aid are not actually genericized, that's a myth, they're in no danger of being genericized because people know they're trademarks.