Fiction picture books:
The story in a picture book must come to a natural and logical conclusion. The action should end at a definitive moment. No plot points should be left hanging. The reader needs to be satisfied with the way the story ends; the main character (with whom the reader is identifying) must solve the conflict by the last page. The conclusion cannot be implied or left open; readers shouldn't have to choose between several possible outcomes.
Some authors try to sum up the message of the book in the last paragraph. If your story is well-written, the reader will know what the character learned without your having to blatantly spell it out. Once the action is over and the conflict resolved, the story ends. Anything beyond that point dilutes the impact of all that's gone before.
As with articles, the end of a nonfiction book is the conclusion of all the information you have presented. However, with books you have an entire chapter to make your point. Many authors title their last chapter with a question, such as "Where Do We Go From Here?" or "What Does the Future Hold for the Amazon?" The body of your chapter will answer this question, drawing from the facts in the book and posing possible solutions. If you relate the subject to the reader's own life, he will continue to have an interest in the topic long after he finishes your book.