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.