It's tough to get published these days. Before submitting to an editor or agent, you might consider spending some money on an expert consultation for your children's or YA book manuscript. Several topnotch professional editors have left the industry to set up their own freelancing businesses:
Cynthia Leitich Smith maintains a full list of critique services including those offered by ex-editors. If you know of other freelancers who used to work as an editors in publishing houses, drop their names and URLs in the comments and I'll add them.
Laura Atkins Lee and Low / Children's Book PressContact editor Alvina Ling for information about Sangeeta Mehta, who used to work for Little Brown. Summer Dawn Laurie, formerly with Tricycle, is also available for editorial input. Email her at sdledits(at)comcast.net.
Deborah Brodie Roaring Brook Press / Viking
Sarah Cloots Greenwillow
Kara LaReau Scholastic / Candlewick
Amy Lin Little Brown
Judy O'Malley Charlesbridge / Houghton Mifflin
Stacy L. Whitman Mirrorstone / Wizards of the Coast
Cynthia Leitich Smith maintains a full list of critique services including those offered by ex-editors. If you know of other freelancers who used to work as an editors in publishing houses, drop their names and URLs in the comments and I'll add them.