When I discovered Richard McGuire's incredible kids' books, it blew me away that titles from just a few years ago could already be out of print. [Which isn't the same as being unavailable to buy, of course, but still.] There are thousands more beautiful, memorable, funny, obscure, famous, even classic kids' books that have gone out of print.
Fortunately, there are a few people working to bring some back. The New York Review Children's Collection has set out to reissue 8-10 such titles/year. So far, there are 24 in the series, including D'Aulaires' Book of Trolls, an overlooked complement to the couple's classic D'Aulaires' Book of Norse Myths, and Wee Gillis, the adventures of some Scottish kid as told by the creators of Ferdinand The Bull, Munro Leaf and Robert Lawson.
Kids' Books That Never Grow Old [washpost]
Browse The New York Review Children's Collection Titles [nybooks]