Am I writing a chapter book?

A chapter book is like Junie B Jones. Short, simple chapters with a lot of illustrations for readers who are just starting to progress to long narratives. The characters are usually around K-4th grade. Maybe 800-1200 words per chapter, depending on the complexity.

MG is more complex, like Percy Jackson. Any illustrations are supplemental. The word count rises to around 50-60 thousand.

It has to do with simplicity of story and language, too. Chapter books are fairly linear, where MG books can have more twists to explore the world.

A problem in a chapter book is something that could be explored in an episode of a kid's cartoon. Something like the Magic School Bus. A regular MG novel would be more like a season's arc of a show. There are more complex characters and side plots that may or may not tie into the book's plot.

The first Junie book was less than 7,000 words and it was about Junie learning not to hate riding the bus. Junie was 5 years old and spoke like a baby. She has a series of books, but they're not really connected to the point that you couldn't read only one in any order.

The first Percy book was over 80,000 words and it was about Percy coming to terms with being a demi-god, saving his mom, making friends and enemies, locating a lost thunderbolt, uncovering a plot by another boy at his demi-god camp, and setting up the entire Percy series that would come after.

Lower middle grade is definitely a thing. (Think something like the long-running serials like Animorphs. No illustrations, more complex than a chapter book, and tops out in the 30K range.)

Out of curiosity, how old is your main character?

Chapter books are intended for readers ages 5-8, just exploring reading on their own and not able to sit for a complete middle grade. Middle grade is ages 8-12, confident readers with a longer attention span and more freedom to explore the world. Often, the main character of either is at the top age or two of the reader range. (So 7-8 for a chapter book.) That's why Cyia asked.

I suggest reading a chapter book and then a MG book and see which tonally and thematically your book most compares to.

But right now it sounds like it could be lower MG - which works with your current wordcount.

It's good to ask questions and get a feel for where your book may fit in the market, but it's even better to study and know the market yourself. Look for chapter books (which span a large range, with some books for kids who are just starting to read books on their own (with lots of illustrations) and some for kids that are just about ready to move on to MG (minimal illustrations, less white space on the page)) published within the last 5 years (Scholastic's Branches line is a good place to start, then move on to Clementine, Judy Moody, Stink, and the like). Most have fewer than 15,000 words, though, even at the higher level.

Yes, I agree with reading chapter books and MGs and then getting a feel for both. Go to the library. Read the Junie B. Jones books, which are chapter books for the youngest readers. Then get into some tried and true MGs like stuff by Kate DiCamillo and Christopher Paul Curtis. Note the word count and depth of plot for each genre. You'll soon get the feel. When in doubt, ask the librarian for help.