Australian Society of Children’s Book Writers & Illustrators – I’m not sure how useful this site will be but as it concentrates on the Australian sector of children’s writers I have to include it here.
Children’s Book Council of Australia – This looks like an informative site with links to publishers etc and basic information about getting published.
YAWrite – This is a critique group. I’m told this is a group for adults (over 18) who write for children and they take all age groups from picture books right through to young adult.