People who are unfamiliar with children's book publication find it interesting that the writer and artist do not usually collaborate. The outcome is a collaboration—a co-created piece of literature—but the process isn’t necessarily so. It is the role of the illustrator to be inspired by the words and bring their interpretation—their story—to the book.
In some cases, the designer at a publishing house will request input from the author with respect to confirming accuracy and intent of the text or when an illustration needs to carry part of the story as defined by the author. However, the choice of the illustrator, the medium they work in, and the content of the illustrations are elements left to the art department and the creative mind of the illustrator.