SCBWI: the Society for Children’s Books Writers and Illustrators - they have many resources and events. They have a large number of critique groups you can join, webinars, events, and both regional and national conferences. It's a great place to network, learn, get critiques, and find community.
KidLit411: they have a website full of information, but they also have a FB group that is a great place to ask questions.
Underdown/The Purple Crayon: a website run by Harold Underdown, a long-time editor and kid lit industry expert - features a lot of great information.
Storystorm: annual month-long event (FREE) where participants attempt to generate at least one picture book idea per day.
12x12: an online community and webinar series that encourages members to complete or revise one picture book draft per month.
NaNaWriMo: annual month-long event where participants attempt to finish a draft of their novel.