So far I've been lucky in that there doesn't need much editing in Dr. Seuss. Eventually I'll probably find a line I won't cross, but at the moment I'm not sure where it is.
Something like that, Horton Hears a Who isn't ringing alarm bells yet. Most things just sail right over her head so I don't address things unless she asks. She's not shy about asking, but even then it can be difficult to frame a response in a way she'll understand. The wife's solution is to not sugar coat anything and just tell it as it is. It usually involves using really big words that our daughter doesn't understand yet. My daughter will shoot back a puzzled and annoyed look and then go about her life like nothing happened.
Books aren't nearly as bad as movies though, and video games for that matter.