We make a fuss about adult bestsellers. But classic children’s books keep selling year after year. “Chris Van Allsburg’s The Polar Express, which has sold more than 4 million copies since 1985, magically reappears on the bestseller list every Christmas. The Poky Little Puppy has racked up sales of more than 14 million since 1942. Goodnight Moon (1947) is still going strong at 6 million. These are among the books that never seem to date or disappear.”