The 3 most important components to your submission will be your cover letter, your manuscript (text only), and a dummy of your book (optional, but helpful). Even if you are not the illustrator of your book, remember that the dummy shows the editor who gets your submission how you are thinking of pacing your story. You have to convey to him/her just how serious you are about your book, so even if making a dummy adds more prep time, do it to make your submission stand out from the hundreds and thousands they receive per month.
Publishers may ask for other things, like a biography or a market analysis for your type of book. Who are you? Why have you written this book? Why do you care about children's books? And how do you think the current market lacks your type of book? Who will buy your book? While I think the latter question is a little unfair to ask of us, just make your best effort and speak from the heart. Speak it flawlessly, though, make your cover letter your priority, and your manuscript and dummy perfect.
In the next few posts we’ll take each in turn, starting with the cover letter, which to this day still somewhat eludes me as to how to write a great one!