I have several friends who are submitting manuscripts to various venues, some without the support of critique groups. I feel for them and it makes me even more grateful for my group. For me, nothing beats a physical group, the sincere advice, sympathetic coos and enthusiastic cheers offered in person. But when I submit, my insecurity rises to atomic level and I need additional support. Two children's writer's venues I've found extremely useful are the Verla Kay and Society of Childrens Book Writers and Illustrators' discussion boards. On Verla Kay, members can post questions in threads covering topics like genre, marketing, and craft. VKers helped me shape an agent-worthy query and while I waited, I researched query response time on their agent list. Some VK members are published authors who generously share their experience. Once, I was thrilled when Maggie Stiefvater answered my question and that was after she'd became a YA fantasy star.
SCBWI offers a similar discussion venue but you must be a paid member to participate. Most serious children's writers join the organization which has been the hub of my writing community, supporting regional critique groups and conferences. SCBWI's website provides helpful resources for beginning writers and grant opportunities. Writers use the discussion board to form physical and online critique groups, network, inform and learn. When I sold my first story, I sought clarification on contract terms and received a helpful response from a legal expert on SCBWI.
I'm sure there are other valuable websites dedicated to the children's writing community. The best thing about virtual venues is showing up just as you are and not worrying about bed hair or that coffee stain on your shirt. I've found the online writing community kind and encouraging, so no excuses, come out of your cave, turn on the computer and click!