Evil can be incredibly deceptive. In a nonfiction book a reader is more alert to any false teaching. A nonfiction book has a straightforward goal, and one can easily debate wrong arguments. However, a storyteller weaves his philosophy in and through the medium of a good story. Undiscerning readers are not aware of all the false truths slipped into the story.
Fiction can be a dangerous thing.
On a final note, we should be aware of the different forms in which fiction comes to us. It can be even more dangerous to read fiction and assume it as fact. May we encourage you to examine your family's books and put them to this test. You will be exercising discernment and teaching your children how to have discernment. Without discernment, we are tossed about and manipulated by the world and Satan at will.