I have been thinking about your comment "A funny animal sound book would also be great for (the very short kids)." and I am curious--how much harder is it really for a new writer to sell younger, board book style picture books (maybe not Click Clack Moo, but a more basic, "the cow goes Moo" style book). I have heard from other sources (I think Harold Underdown talks about it a bit) that board books are more often done with established or in house writing. I am sure that good writing and a great hook can work wonders, but is this an even more difficult proposition than normal?Yes.
Board books look cheap, don't they? They're small, they don't have a jacket, they aren't printed on any of the really nice paper (because they're going to end up in a toddler's mouth)...
So here's the thing. Thin paper is cheap—that's why they use it for newspapers. Board books are printed on cardboard, and it's not cheap. Regular paper is easy to cut at the printer—snip snip, big, one-size-fits-all blades. Cardboard must be cut with a specially made and regularly sharpened die like a cookie cutter (have you noticed those rounded corners?). Making those isn't cheap, either.
Board books are not cheap to make. Alas, they continue to look cheap, so people simply won't pay very much for them.
This means two very important things:
1. Paying somebody an advance and royalties for a board book is difficult. It makes so much more sense to convert a book you've already published in another format into a board book. Then you pay royalties, but no advance. Or you could pay the author/illustrator a flat fee. Or, best of all, you make an editor in-house knock out the text and have a designer in-house knock out some illustration. Then you don't have to pay them anything.
2. The profit margins are so small that board books only make financial sense if you can print a whole bunch of them. That means they have to have content you're sure is going to be popular. There's no gambling on content in board books. They're a gamble already.
Take my advice and don't present a manuscript as a board book just because you think it'd be cuter that way. Starting a book off as a hardcover picture book is always more profitable for the publisher, which means the acquisition pulls more weight for the editor, the book gets more attention, and it's more profitable for you.
So board books are hard, and they're not lucrative. I still wish there were more great ones.