I would have no hesitation giving adult learners Dr. Suess to read, for instance.

I have a few Korean picture books, but they're slow going for me. I feel like picture books tend to have a lot of kid-oriented language and onomatopoeia, and Dr. Seuss in particular uses so many neologisms, so it's a genre primarily aimed at readers/listeners who are already relatively fluent in the language and only learning reading/story. /two cents, obviously YMMV!! :-)