Suggestions for book/lecture on improving craft for writing Middle-Grade books?

I can see that my next set of writing is going to be early Middle-Grade books (for various reasons, including wanting to give that community more vehicles to fall in love with reading as I did in 3rd & 4th grade). I have over 30,000 hours of academic & professional writing under my belt & a few thousand hours of adult non-fiction book writing, but none for 3rd/4th graders. I would welcome any suggestions of great writing craft books/videos/lecture - for general fiction and/or specifically early middle-grade fiction. Thanks!