Father shapes a bedtime story to wakeful Alex's comments. He begins with a boy (pictured as Alex) walking in the jungle; but when the boy closes ``his weary eyes,'' Alex pops up: ``The boily, boily jungle made me thirsty.'' So it goes, until Father finally captures Alex's full attention with a trip to the moon, with the boy followed by a mild-looking but many-horned ``thingamajig.'' This time, when the boy makes his way back home to bed, Alex, too, is ready to call it a night. A jacket photo suggests that Father is the author's self-portrait, while Alex also bears a strong family resemblance. The improvised story is authentically haphazard; meanwhile, the book is a model of creative interplay between parent and child, a theme beautifully extended in the illustrations. The more formally bordered bedroom scenes include a toy dog that joins Alex in Father's story; the story-within-the story illustrations are imaginative, dreamlike. Like Angela Johnson's Tell Me a Story, Mama, an unusually perceptive portrayal of healthy interaction. (Picture book. 3-7)