Chapter Books range from 5,000 to 20,000 words but most are under 12,000, the MC is often between 7 and 10, the chapters illustrations, the books tend to be in 3rd person, the chapters tend to be short and contain a scene . Middle grade starts about 25,000 but averages closer to 40,000, the MC is usually between 10 and 13. the books don't tend to have illustrations, can be in any POV, tend to be a lot more descriptive and chapter lengths vary more.
Do the above generalities help?
Rainbow fairies and Critter Club are chapter books. Was there an MG series you could compare to as well?