SOCIETY of CHILDREN'S BOOK WRITERS and ILLUSTRATORS - A huge site dedicated to helping people write for children. When you join SCBWI, you have access to their complete site!
THE INSTITUTE of CHILDREN'S LITERATURE - This is one of my go-to sites for help. You'll find articles, a free newsletter, forum, and alot more here. You don't have to take the correspondence course to have access to the wealth of information here but the course is worth taking!
CBI CLUBHOUSE - This is my personal favorite! You'll find everything under the sun for the aspiring or accomplished children's writer without joining. Like SCBWI, when you join you have complete access to the complete site including how to make book trailers and book apps.
THE PURPLE CRAYON - There are many articles about writing for children here plus a helpful column by children's author, Margot Finke.
PREDITORS AND EDITORS - This site can tell you which publishers are legitimate as well as giving you warnings about some companies.
DIGITAL KIDS AUTHORS - This website has information both paid and free on all things pertaining to book apps.
TEN MORE WEBSITES THAT HELP CURE WRITER'S BLOCK WITH WRITING PROMPTS - I've recently found this site run by seasoned professionals. You'll also find webinars and more here.
KIDLIT 411 - This is a portal into everything "kid." It has links to editors, agents, and lots more. You really have to explore this site!
RACHEL BURK'S RESOURCES FOR CHILDREN'S WRITERS - I realize that this is a blog but it has helpful articles, publisher listings, editors, and more!
KIDLIT TV - You'll find everything you need at one handy place. Learn how to make book trailers, conduct interviews, and more.