I have over 30 years' experience in the publishing/writing industry, working as everything from an in-house editor to an investigative reporter to a novelist to a medical/technical writer to a screenwriter. I've been an independent contractor for 24 years working as a freelance editor (developmental and line editing), writer (fiction and nonfiction), ghostwriter, and copy editor.
Once you have narrowed your options down to a few editors, five or less for example, set up some initial contact with each of the children’s book editors. Start by contacting them and see if they can answer your core questions via email. Find out if they are willing to chat with you by phone or skype about your project when you are ready to make a decision. Ask for them to specifically identify what children’s book editorial services they will be able to provide.
An extensive critique of my first novel led to major changes in the format. I was very fortunate to have an experienced novel writer to give a detailed analysis, with corrections. I did not fully appreciate, at the time how valuable this process was, but do now. You need to acknowledge that there are likely to be inconsistencies leading up to the final manuscript and be prepared to make drastic changes. An editor is attuned to picking up on these, where you have accepted the script , even after numerous re-writes!
Developmental Editing helps you fine tune the sequence and the order of your book. Have you presented the information in a format that makes sense to the reader; does each piece of information build upon previous material? If you’ve had a few people read drafts of your book and they’re confused, you need developmental editing. A developmental editor may even be able to help you uncover features in your work that will create a powerful experience for your readers.
For editors who are charging pennies for what should be hours and hours and hours worth of work: I am saddened that you would ruin the market for those who have the expertise and ability to charge what it’s worth. You see, an author whose book needs a whole lot of help will see your rock-bottom prices and think that’s the norm. But the reality? That’s not normal. It’s not normal to charge sweat shop rates for something that requires top-notch quality.
Obviously there is a big difference. I actually started with screenplays (with some mild success) partly due to hearing that as long as you have a good story, the grammatical errors won’t be a big deal. Well, that was not true. Maybe if a producer liked the story or I was already established but every contest I entered always came back with feedback about the grammatical errors. Even if I won or placed as a finalist, I always received critique on that. Very little is spelling error, it was more about structure, etc.