Re: Where do you get your children's books?
I had a lot of paperbacks from my non-mom days so I posted them to paperbackswap.com for credits and I got some fantastic kids books from there, some seemingly new, in hardcover. I think you get 3 free credits for joining.
Also my local Salvation Army is softcovers 3 for .99 cents, hardcover for .50.
If you're willing to pay a little more, TJMaxx (Marshall's too maybe) has discounted books.
Craigslist often has people selling boxes of kids books if you don't much care what you get. (We don't do these because we avoid Disney and other branded toy books)
I run the Frontier Wholesale co-op in February, May, August & November