Condition, condition, condition is what the experts say. If you are collecting with an eye on future sales or institutional donations, sellect the best condition you can afford. Pass up anything less than your upper limit, or purchase a very cheap placeholder that you can read and discard.
Unless a title is extremely rare, extremely old, and extremely significant, a children's book is considered collectible only when it is in strictly graded Very Good or better condition. You will hear that children's books are always in terrible shape and that condition does not matter in this field. This is not true. It is true that the absolutely pristine books seen in collections of Modern Firsts appear less frequently in children's offerings, but, as with other fields of collecting where books are expected to have been read, very nice condition is still important.
Books are graded by professional dealers using the AB guidelines, from the now defunct AB Bookman magazine. Guidelines for jackets run parallel to these. There has been a huge amount of grade inflation on the net: Fine books should have no mentionable flaws, yet Fine ex-libraries with cracked hinges appear all the time. On the other hand Good, in bookseller language is not very "good" and Ebay booksellers sometimes use good to mean a nice book! Very confusing. Unless you are dealing with a professional, it is always best to get an exact description of specific flaws rather than a condition grade. Call the bookseller and have them look at the book and tell you the worst flaw that they see. Jpgs can be very deceptive, by accident, ineptitude, or design. Our jpgs can be enlarged to show flaws, and we always photograph the entire jacket against a dark background so that you can see the edges. Still our written descriptions and our consistent AB grades are really more informative.
Of course, you can collect books in any condition you prefer. Personally, I enjoy scrawly little inscriptions written in beginner's printing, but, for most people, these are defects, which detract from the value of the book. We have customers who are assembling large private research collections of certain genres and accept VG ex-libraries in nice cleaned jackets as placeholders; it would be almost impossible to build their collections otherwise. However, these books are of value only in the context of the collection. If you ever have to sell your collection, bookdealers will be reluctant to purchase books in Good or less condition from you. They know that the resale value of most books in Good condition is uncertain and that the books may take a long time to find a buyer.
Ex-libraries and remainders
Because the original condition of an ex-library book has been greatly altered, a juvenile or picture book ex-library is not considered a collectible book. Certain dealers on the net work on a pure here and now, supply and demand model and thus several years ago they used to put outrageous prices on popular children's ex-libraries; you will still see the occasional left-over $250 book "withdrawn from suburban library". When these books were reprinted, the prices of the ex-libraries fell dramatically. However, if a rare book has come from an uncirculated Special Collection and thus has few marks and little wear, it still has some value; the same applies to scarce children's reference titles.
All of the above generally applies to publisher's remainders, except that remainders tend to be newer books and thus almost never have value. Remainders are indicated by a slash or dot on the top or bottom of the page edges, and occasionally by a spray, or not-for-resale stamp. If you see on online listings that a book has been remaindered, be very careful in purchasing a book that appears from the listing to be a non-remaindered copy. Although a book with a small dot on the bottom edge is less unsightly, the dot should still be mentioned.
Books without jackets
Actually jackets have been used on children's books since the mid 1800's and were issued on most early 20th century books. Initially, they were plain covers made to protect the book on the bookstore shelf. I have found jackets like these with lovely designs, but they were made to be discarded. As time went on, jackets began to take on some of the functions which were originally incorporated in the book: an attractive cover, an author biography, a title list, a price, a book advertisement, perhaps a date.
Unfortunately, there is no clear cut-off date before which a book is collectible without its jacket and after which it is considered incomplete without its jacket. As a general rule, books published in the early 20's and before are not identified as missing their jackets, while after that time, the absence of a jacket is noted (VG/0). As the century progressed, more and more of the information that used to be contained in the book itself was moved to the jacket, and the jacket became important in identifying publication data, as well as a display for the artist's work.
How consistent are condition grades?
Children's specialist dealers who also do business offline with catalogues, shows, and private customers grade very consistently using AB guidelines: that is if you gave each of them the same box of books to grade, the grades would be nearly identical.
With an established dealer, you can usually assume that any flaws mentioned are the worst ones (i.e. if there is a quarter inch closed tear in the jacket mentioned and no mention of the hinges, the hinges are not broken). The written catalogue style was to note only flaws in a condition description, assuming that the book had the good points of its condition grade. The internet has changed this, adding reassurances like "straight and clean". We have changed with the times on newer listings, but the old system was more accurate... if I neglect to say a Near Fine book has clean pages, will the customer worry that it doesn't?
There is a wide variation in grading standards on the net. I trust descriptions that mention small flaws and do not use overblown adjectives or stock phrases, such as "good for its age" or tricky ways of avoiding the word "ex-library", such as "withdrawn from suburban lending room of exclusive private school." Dealers who use grades like Very Good +++ are generally unreliable. If you do not know an online dealer, you need to pay more attention to the specific details of condition and pretty much ignore the grading.
Dealers who primarily hand-sell books at shows and by appointment write shorter condition descriptions on their book listings, but their grading and prices reflect the book's condition. It is perfectly acceptable to email or phone for more information. If you seem to be working with an experienced dealer, say "What are the worst flaws in the book, in the jacket?" If the dealer seems unsure, just ask what the particular parts look like, "What does the top of the spine look like?" etc.