I think I've referenced this excellent blog by a children's book editor before. Two recent articles of universal writer interest regarding submissions.
Today's Easy Question
Can you send in a handwritten submission? Her response is absolutely in line with our experience at ECPI - only children and incarcerated felons do this. Yep, we do get subs from prisoners, handwritten in pencil on lined paper, due to their restricted access to computers.
I Don't Know Why I Love You Like I Do
Even multipublished authors get rejections of new proposals from their existing publisher. No matter how great the writer overall, not everything they produce is great.