Say a person has a fun middle grade book, but decided to break it into many picture books instead. Both make the author happy. The author isn't sure which format would make agents and publishers happy. Should author mention it in any way in a query? Like..."This picture book is first in series of many episodes with this character..." in hopes that they could assume it could be changed into a chapter book? Probably not, right?I can't quite get past your first sentence.
You broke your middle grade manuscript into many picture book manuscripts?
Point 1. Picture books are not just shorter.
They're for a younger audience. Which means the writing and pacing and voice are different. I got a picture book manuscript just last week that clearly had chapter book voice and pacing. The author wanted to do a series of picture books. I said no, and I wondered if the author knew how to write for either age group, since she doesn't seem to see a difference between them.
Point 2. Middle grade books are not just longer.
If your middle grade book was that easily chopped up into picture book-length stories, it must have been a hell of an episodic book-- a collection of short stories, in fact, rather than a cohesive narrative.
Obviously, I can't tell for sure about your work, since I haven't read it. But from this description, I would have strong doubts about it working as a picture book or as a middle grade novel. Take it from me, they are not equal possibilities for anyone's manuscript. One or the other age group is going to work better, and you will be a stronger writer when you figure out which one.