I did a bit of research on the differences between the two and got some pretty useful information. I read my novel again and realized it was just too mature for the middle grade group. I've finally accepted that I was targeting the wrong group. Right now I'm writing on, with young adults in mind and I must say, it's great to know exactly where my novel fits.
Looks like I won't be needing those illustrations after all. I do look forward to the cover design, though.
For those of you who are confused by the two genres (like I was), here are some links that might be useful: