I have been working on a women’s fiction for a while and this is ultimately the genre I want to write in, however, I also have a stand alone MG that follows a group of kids as they discover the rich history they can learn from the veterans around them instead of just memorizing facts from a book. The news recently reported more than 100 WWII vets die every day so now I am feeling this needs to move up in priority. I have read a lot of posts about how important your debut work is and I am wondering if low sales in MG (if it ever gets published) would be a negative for me when querying the other work. Also, is it wrong to query two vastly different projects at the same time?
Editors look at sales figures to try to predict how the next book will do. Propose a book on kale recipes and your previous book 101 Uses for Weird Vegetables, which appeals to the same audience, will be used as a predictor of interest in the new book.
You can see where this is going of course.
There is almost zero crossover between a middle grade non-fiction book and womens fiction. Even if an adult reads both, it's for very different purposes.
Also, middle grade is sold very differently than womens fiction. MG buyers generally aren't the readers, they're teachers, librarians and parents.
Thus, your mg sales figures won't be considered a reliable indicator for your womens fiction sales.
That said, nobody gets a pass on crappy sales figures these days.