As Melissa Wiley reports at Here in the Bonny Glen, there are several places where you can still find unabridged (original) versions of the prequel books to the Little House series. This is another source from an earlier post of hers. And another. If you don't know what happened to these books, she explains in this post that the publishers have decided to reissue the books with huge chunks taken out. She says:
The abridged editions of my books and the Caroline and Rose books will be released with new covers this summer. They are significantly shorter; in some cases more than a hundred pages have been cut from the original edition.
Why? Who knows. Well, ok, the publisher knows. It was a business decision.