A number of appealing picture books have been published recently, dealing not so much with a single central event as with the relationship between a pair of characters. They often appear as chapter books, divided into three or four separate adventures instead of one longer story. Arnold Lobel's classic Frog and Toad stories have had something to do with the evolution of this genre, but a number of fine stories have come out more recently. And now Oneal, acclaimed for her novels for older readers, throws her hat into the ring as well. Here, Walter is the big brother, Maude the little sister who's always trying to join his games. We follow them through Walter's kite-making project, his creation of a backyard tent (with a sign outside that says ""No Girls""), Maude catching a cold, and her creation of an imaginary friend to replace her reluctant brother (who suddenly starts missing her). Oneal's book is funny, believable, and tender at the same time. Chambliss' illustrations are nicely detailed--with Tinkertoys sticking out of Maude's pockets and dinosaur drawings taped on the kitchen wall. Like the best of the ""relationship"" books, this one goes beyond specific brother-and-sister issues. It's a warm, heartening depiction of friendship.