"Thinking too much about chalk," and the full texts it cites: Thomas Huxley's "On a Piece of Chalk" and GK Chesterton's "A Piece of Chalk".
Did you know James Joyce wrote a children's book (sort of)? Patricia Highsmith wrote one too. So did James Baldwin (not to be confused with James Baldwin the children's book author). Eugène Ionesco wrote four stories for young kids. Graham Greene also wrote at the very least four children's books (and possibly more). Other unlikely children's book authors are Aldous Huxley, E. E. Cummings, Chinua Achebe (2, 3, 4), Eleanor Roosevelt and Gertrude Stein. Author Ariel S. Winter has written about all these books on his excellent blog We Too Were Children, Mr. Barrie. On his Flickr page you can look at scans from these books, sometimes even the whole book.