For Seuss it’s depictions. For Splash it’s way more including the movie, the situations in the ride, and the fact the stories were taken from slaves and then sold without them receiving any of the money.
But I can’t get too into it rn as I’m in line for Muppetvision.
I'd also add that Zip-a-Dee-Doo-Dah's main chorus is derivative of a pre-Civil War song which was smack dab in Minstrel Shows. An that song is universally associated with the ride and movie since it's the main theme song.
As for If I Ran the Zoo, as others have said, what's happening is the publisher removing the books with offensive chariticures. Considering those are nowhere to be found in the play area, then there's nothing to worry about.