The Society of Children's Book Writers and Illustrators (SCBWI.org) is the largest writing organization in the world (seriously) and many successes can be attributed to being a member/participant. As Illustrator Coordinator for the Southern Breeze region (Alabama, Georgia, and the Florida panhandle) I can confirm the SCBWI has opened many doors for me. And many writers and illustrators say they never would have made it in the kidlit biz without it. Read about many success stories at Ink and Angst: Gate Crashers Ask Why SCBWI.
And if you live in our region, it's not too late to sign up for our Fall Writing and Illustrating for Kids (WIK) conference in Birmingham, Alabama on October 11-12, 2013. Go to Southern-Breeze.net.