Kathleen and I are on the same wavelength tonight. Anyway, your post got me digging out some old files as I once was involved in writing the text for an "accordion" Glow in the Dark format book idea a retired toy manufacturer wanted to sell. We did get the chance to pitch the idea in a face-to-face meeting with an editor at Golden Books.You didn't state what type of children's book you have in mind, or for what age bracket. Or if you have a format in mind, say, a glow book, or a hard cardboard die cut, etc., for young readers.
What I learned from our own venture into this is that publishers of children's book sometimes buy copyrights, and they spend a great deal of money obtaining these rights. What they end up with is a vast library, with major characters they can use in different formats, so of course, they're going to be thinking about how to use those characters they've paid for. Do you have a neat idea - format and storywise - that could fit into something like that? They also work with "packagers," or what I term "think tanks" - companies that focus on revolutionary ideas in terms of packaging/design. For instance, a "pin book," in the shape of an apple or a bell, that the child can read and then wear as a pin.
The following is a Web page with a bit of info about pop-up books & their designs/designers: http://www.library.unt.edu/rarebooks/exhibits/popup2/present.htm.
Do you have a "patentable" idea for a children's book? If so, a packager might be interested in the project - but you need to thoroughly research in terms of technology and application the idea you come up with before they'd work with an outside creative person. A few years back Intervision Inc. in Santa Monica was one, as was White Heat in Santa Fe, New Mexico. These packagers produce a "model" for the publisher, and then the books are most often produced outside of the country, then shipped to the publisher for distribution.
Something you might want to do if possible is attend a book show. One to maybe consider is BookExpo America. Check out the Web site at: www.bookexpoamerica.com.
Lots of exhibitors at this type of thing - publishers and wholesalers, I suspect - and more info under one roof than you could gather quickly on your own (plus inspiration, yes?).
And if your idea is to write the next Harry Potter series, then I've just wasted your time with my too-long post! Just thought I'd share what I learned.... Good luck!