WriteOnCon is an online children's writers conference that takes place in August each year. It began in 2010 and had over 11,000 attendees that first year (my mind can only boggle at the number of attendees in subsequent years as word spreads).
This year the conference will take place on August 26th and August 27th so clear the date in your diary. The schedule hasn't been announced yet, but I imagine they'll have lots of sound writerly advice with posts from published authors, agents and editors. They usually have live Q&A events, and last year they featured Twitter pitches with literary agents for the first time (my Twitter pitch was commented on in a session - it felt a bit surreal to see my Tweet onscreen and know hundreds or thousands of other people were seeing it as well).
Half of the fun is interacting with other writers in the forums (which usually open ahead of the conference itself). If you're a brave soul, you can post your query, first 250 words and/or first five pages for critique. You might have a Ninja Agent pop into your thread and make suggestions, or even PM you with a request to see more.
The conference & forums are well-worth a visit, so I'll hope to see you over there. (My username in the forums is 'Netz', if you're looking for me.)