Before Eric Carle, there was the brilliant Leo Lionni. I am so in love with his books. They are seemingly simple, very zen-like. A beautiful match of few words and crisp images. His short stories carry meaningful messages of character and integrity. It is not surprising to find out that he had a very brilliant career in advertising prior to writing children's books. He headed up the graphic design department at Parsons School in NY and was the art director for Fortune and co-editor of Print. He also worked in advertising at prestigious firms as art director. He had a strong influence on both Eric Carle and Ezra Keats.
Here is what Leo Lionni had to say about his process:
"Inspirational raptures may happen, but most books are shaped through hard, disciplined work. Creative work, to be sure, because its ingredients come from the sphere of the imaginary. But the manipulation of these ingredients requires much more than mere inclination or talent. It is an intricate process in which the idea slowly takes form, by trial and error, through detours and side roads, which, were it not for the guidance of professional rigor, would lead the author into an inextricable labyrinth of alternatives. And so, to the question 'How do you get your ideas?' I am tempted to answer, unromantic though it may sound, 'Hard work.'"
He didn't begin writing and illustrating children's books until much later in his career. In fact, his first book was developed to entertain his grandchildren on a boring train ride.
Here is a wonderful link where you can see more of his books and learn more about him.