The average word count for a children's chapter book can vary depending on the age range and reading level of the target audience. For children between the ages of 8 and 10, chapter books typically range from 5,000 to 20,000 words.
The length of the book primarily depends upon the complexity of the storyline, the theme of the book, and the intended reading level. Stories aimed at younger children (ages 6 to 8) tend to have shorter and simpler sentences while stories meant for older children (ages 10 to 12) tend to have longer and more complex sentences.
Typically, chapter books for 8 to 10 year old readers have about 8 to 15 chapters, in total. Each chapter usually has approximately 2,000 to 3,000 words, depending on how much action and dialogue is included.
Overall, it's important to keep in mind that word count isn't the most important factor in writing a children's chapter book. Engaging characters, an exciting plot, and easy-to-read writing style are much more significant in catching the reader's attention and holding their interest.