I found this article really helpful — great book examples for each category, too.
Five Kinds of Nonfiction by Melissa Stewart :: School Library Journal

“Here is an idea I love that may or may not be true: Some books have a centripetal force— they suck you in from other books. Some books have a centrifugal force — they spin you out to other books.”
The books that suck you in and the books that spin you out :: Austin Kleon

“Writing for children means writing about children. Chapter books are often about kids learning how to navigate conflict with peers and adults, middle grade is often about exploration and imagining a world where you’re making decisions without your parents, and young adult fiction is often about navigating emotional complexity. But they’re all about kids navigating their worlds and trying to get the things they want. Sometimes that needs to involve adults, sometimes it doesn’t.”
How to Write Adult Characters in Children’s Books :: Nathan Bransford

“So how do we write picture books that show character change without explicitly stating the lesson? It’s a rather simple answer: let the character have some realizations and then act upon them. At the same time, do not explain what the character is learning.”
Picture Books that Show Character Change :: KidLit.com

Joanne and I were a part of the Class of 2k12: children’s authors who debuted in 2012. This Instagram post is spot on: “This period of success is the culmination of years of hard work and rejection. A lot of rejection. From agents and editors: kind rejections, some abrupt rejections that bordered on mean, some ghost rejections, and maybe most heartbreakingly, some almost yesses that turned into rejections. At one point, before even my first book published, I logged nearly a thousand rejections. I stopped counting, but there have been many, many more since.”
Never Give Up! :: Joanne Levy

“It doesn’t pay to pretend that we’ve figured it out before we have. It’s counterproductive to adopt a brittle attitude in the face of criticism. In fact, during this stage, ‘you’re not that good,’ is precisely what we need to hear, because it might be followed with insight on how to get better.”
You’re Not That Good :: Seth Godin

Thank you, Gary Paulsen, for everything. “Gary Paulsen is a national treasure, a landmark author whose many books don’t just transfix and entertain, they change the course of readers’ lives. Hatchet and his other edge-of-your-seat stories—many of them inspired directly by his own experiences—have shown reluctant readers the world over that reading is itself an adventure. His books have helped readers overcome fears in their own lives and instilled in his millions of fans through the decades a passion for undertaking their own personal feats of daring and courage.”
Obituary: Gary Paulsen :: Publisher’s Weekly

 

Writing is a very silly business at best. There is a certain ridiculousness about putting down a picture of life. And to add to the joke — one must withdraw for a time from life in order to set down that picture. And third one must distort one’s own way of life in order in some sense to simulate the normal in other lives. Having gone through all this nonsense, what emerges may well be the palest of reflections. Oh! It’s a real horse’s ass business. The mountain labors and groans and strains and the tiniest of rodents comes out. And the greatest foolishness of all lies in the fact that to do it at all, the writer must believe that what he is doing is the most important thing in the world. And he must hold to this illusion even when he knows it is not true. If he does not, the work is not worth even what it might otherwise have been.
— John Steinbeck, Journal of a Novel: The East of Eden Letters

Read more quotes I enjoyed from the book here.