Ali, 9000 words is on the upper end of the chapter book spectrum. MGs are usually around 25-45k, even longer if it's a fantasy. But more than word count, it's content and reading difficulty that will better define what you have.
Hairaplenty, yes, the overview was a one sentence concept pitch. I'm on my phone right now but later I'll dig it up and post the overview here to give you an idea. The proposal was about 3 or 4 pages, including character bios, and 3-sentence book synopses. I also had a complete ms (the initial sub package was only a sample chapter, but after the editor expressed interest I wrote the whole ms for her to take to acquisitions), and art samples.
ETA: Here is the series overview.
In the city of Fowladelphia, one chicken stands against injustice. Armed with amazing abilities, a super-snug super suit, and a plucky sidekick, Kung Pow Chicken is the ultimate superhero...or at least he would be if not for scary clowns, leotard wedgies and a super over-protective mother.