Found this intriguing article at The Guardian. It's called How to Publish a Children's Book: A Guide for First-Time Authors.
Whether you're a first-time author or not, you're going to find some gems here. This one's our favourite:
Modern editors take word count quite seriously. They rarely have time to thoroughly edit the books they acquire, so if you’ve written a 200,0000-word middle-grade opus, most editors will think, “Who needs that kind of stress?” and give it a hard pass.
Give the full article a read to learn more...