The name “first chapter” may come from two places. One, these books are usually the first books kids read that actually have chapters. Two, the entire book is about the length of one chapter in an adult novel. First chapter books contain some pictures, often black and white.
Beginning readers are proud of the fact they can finally read, and first chapter books are the bridge for these new readers from picture books and easy readers to junior novels. First chapter books have eight to ten chapters and are 6,000 to 8,000 words long. The difficulty comes in developing well-defined characters and a complete story in such a short space. Dialogue is crucial to the success of a first chapter book, lots and lots of it.
Young readers enjoy humor and mystery thrown in with their action, and I recommend a single viewpoint character to prevent confusion and promote reader identification. First person works well for these books but is not necessary.