These six easily read chapters about the four-year-old sister of Russell, one of Hurwitz's favorite characters, are appropriate for precocious readers and listeners as well as for Russell's third-grade contemporaries. Each chapter stands alone, though they are linked by several themes. Elisa, given to easy tears, is dubbed ``Crybaby'' by her unsympathetic brother when she blinks at a photographer's flash, but after she imitates him by jumping from the bureau and breaks her arm, he vows to reform. Meanwhile, there have been incidents with the tooth fairy; with a blizzard when Aldo, Nora, and other familiar neighborhood kids join in the fun of an unexpected holiday; and with a February bathing suit that Elisa can't resist wearing to nursery school- -plus some nice sibling interaction as Russell introduces Elisa to reading. Hurwitz has a rare understanding of four-year-old concerns, disarmingly presented to appeal to both preschoolers and the siblings who feel superior to them. Fans are sure to enjoy this latest entry in a popular series. (Fiction. 4-10)