“Her lovely and original poetry has a flexibility that allowed me the maximum of space to execute my fantasy variations on a Kraussian theme,” Maurice Sendak wrote of the great children’s book author and poet Ruth Krauss (July 25, 1901–July 10, 1993), with whom he collaborated on two of the loveliest, tenderest picture-books of all time. A quarter century after the end of Krauss’s long life, lost fragments of her daring poetic imagination coalesced into a manuscript that alighted to…