Horton Hears a Who (1954): Nobody will believe that a community exists until they all shout "We are here!" Sounds like the Gay Rights Movement.
The Cat in the Hat (1957): An emissary of chaos, accompanied by the gay couple, Thing 1 and Thing 2.
How the Grinch Stole Christmas (1957): a gay outsider is accepted by the community.
The Sneetches (1961): Insignificant personal characteristics, like whether you are attracted to men, women, or both, can create crazy prejudices.
But Seussical, the 2000 musical, is a disappointment. It amalgamates a huge number of books, including some that I never heard of, into two confusing plots -- one for adults, one for kids.
Wait -- those books have no continuity. They take place in different universes, some populated by humans, some by animals, some by other beings.
The secondary plot is promising: Oddball outsider JoJo (here played by teen idol Aaron Carter) is ridiculed for "thinking thinks" and finally sent to military school. He helps save the day without getting a girlfriend.
He buddy-bonds with Horton, but there's not much of a gay subtext between the little boy and the adult elephant.
Except in some local productions where the two actors are the same age, and Horton's elephantness is conveyed through pin-on ears, not an elephant costume.