Beth Revis has an awesome comparison post of YA, MG, and YA/MG crossover.
Calvin & Hobbes has inspired me on more than one occasion...
...and it also gave me hope that Project #3 (Left & Right) is a crossover, and wouldn't necessarily have to be re-written entirely 'cause of the subject matter. In fact, Project #2 (Simon's Oath) could also fall into that category, but only once the narrative has been re-written to be less distant.
Go check out the post and let me know... do you guys think it's an apt comparison?