All writers and illustrators should join.. the Society of Children’s Books of Writers and Illustrators
A go-to site for writing, illustrating and publishing Children’s Books is Purple Crayon by Harold Underdown.
If into Non fiction picture books then take a look at Kristen Fullton’s site – Explore Nonfiction.
A great Young Adult literature site is – http://www.adventuresinyapublishing.com/.
For all things about diversity in children’s literature, go to – WeNeedDiverseBooks.com
Querytracker.net is a great tool when you start querying.
If you are looking for professional editing, then look no further than editor Emma D Dryden of drydenbooks, bestselling author Emma Walton Hamilton, and author and editor Harold Underdown and author and editor Lorin Oberweger at Free Expressions.
Josh Funk’s Guide to Writing Picture Books… https://www.joshfunkbooks.com/resources-for-writers