Key sites that I visit on a weekly basis to help guide me in my writing career in the genre of children to young adults are:

Kid Magazine Writers - http://www.kidmagwriters.com
Voted as Writer's Digest List of 101 Best Writing Sites - 2006
Jan Fields, editor keeps her website up-to-date of industry magazine markets and guidelines; Working Day articles from established and up and coming authors; Editor Speaks and Archive of articles and interviews from editors of many children's magazines.

A Long Story Short - Writer's Ezine - http://www.alongstoryshort.net
Voted as Writer's Digest List of 101 Best Writing Sites
This ezine run by Senior Editor, Denise Cassino and Assistant Editors, Linda Barnett-Johnson and Susan Scott is a wealth of information for many genres. They have watched novice writers bloom under their encouragement, expanding their horizons and entering other markets. An added bonus is their Writer's Lodge that is a place for writers to gather, promote their work, tout their successes and share the joy (or pain) of writing. We have included links to many great articles about writing which are published on Long Story Short. This is a place to own a webpage even if you have your own website. They also conduct the LSS Writing School where you can view and take their online writing courses to enhance your writing.

The Society of Children's Book Writer's & Illustrators - www.scbwi.org
Is the only international organization to offer a variety of services to people who write, illustrate, or share a vital interest in children’s literature. The SCBWI acts as a network for the exchange of knowledge between writers, illustrators, editors, publishers, agents, librarians, educators, booksellers and others involved with literature for young people. The benefits of membership in SCBWI are many. The SCBWI sponsors two annual International Conferences on Writing and Illustrating for Children as well as dozens of regional conferences and events throughout the world. It also publishes a bi-monthly newsletter, offers awards and grants for works in progress, and provides many informational publications on the art and business of writing and selling written, illustrated, and electronic material. The SCBWI also presents the annual Golden Kite Award for the best fiction and nonfiction books and the Sid Fleischman Humor Award.

Writer's Digest - http://www.writersdigest.com
Writer's Digest contains a wealth of information for many genres and includes detail information on: Vendors & Services, Writer's Guidelines, Contests & Competitions, Writer's Conferences, Blogs for Writers, Hot Markets, 101 Best Web Sites, Writer's Forum Books for Writers, and Magazines for Writers.

I also subscribe to various newsletters in the children's market which include:

Stories for Children Newsletter, Children's Book Insider, Writers on the Rise, Tips & Updates from Writer's Digest, and e-News from the Insitute of Children's Literature.

I'm sure you too will find these resources helpful!