I don't mean one shot "adult" humor (such as saying something in a way that makes it sound sexual), I'm talking about overall themes that could be there. Many kid's movies have a moral to them, but are the morals what the people who wrote the movie meant?
I watched "Horton Hears a Who" and by the end of it I could think of many different ways to interpret the movie:
1) Horton is a god. The mayor hinted at it when he said that Horton was invisible, protected them from evil, and spoke to him personally. Also, their world was just a spec and Horton carried it.
2) Whoville is Earth and Nool is space. The animals there are a superior alien race. (this may be a stretch, as the people of Whoville have much better technology.) They have to broadcast their existence to keep from getting meaninglessly destroyed.
3) Pro-life. (even if you can't see or hear them at all, a person's a person, no matter how small)
4) The people of Whoville are kids and the people of Nool are adults. (which I think Doctor Seuss may have actually meant.