A small child sits on his parent's lap and listens to stories. As the parent reads many books to the little one after a short time, these people believe they could write one of these books. It seems so simple because it has few words.
I've written these books and it was anything but simple. The process is complex. Every word has to count when there are fewer words. You have to work hard at this skill but it is something that can be taught.
Check out this article on some of the key factors with children's writing:
You've come to the right place to learn this skill. Books for young people are broken into various categories. These categories are distinct because the vocabulary, subjects and types of books are different in each one.
Usually the first step for a children's writer is to understand the various book genres. Read this article to begin this understanding: