The best children's book writers are not people who have kids, but people who write from the child within themselves.
A query letter should be like a skirt. Long enough to cover everything, but short enough to be exciting.
Most new writers think it's easy to write for children, but it's not. You have to get in a beginning, middle and end, tell a great story, write well, not be condescending-all in a few pages.
Most agents hate prologues. Just make the first chapter relevant and well written.