SWITCHAROUND by Lois Lowry (Houghton Mifflin: $10.95; 118 pp.; ages 8-12).

Sibling warfare is a beaten theme in contemporary children’s literature, but Lois Lowry has such a fresh swing to her writing, this sequel to “The One Hundredth Thing About Caroline” is anything but pulp.

Carolyn Tate and her genius brother J. P. are still at each other’s throats, but suddenly they’ve called a truce. To their mutual disgust, their absentee father wants them to spend the summer with him and his new family in Des Moines. They don’t trust a place that can’t “pronounce its final consonants” and has “dead cattle bones lying around in deserts.” When they realize they’ve been shanghaied--Carolyn as a nanny to 6-month-old twins and J. P. as baseball coach to a bunch of unsavory 7-year-olds--they plot revenge.

What happens is truly funny. Lowry weaves in her moral lessons so artfully that there is little chance for meanness to get out of hand. Mr. Tate and his wife, Lillian, are characters right out of shopping-mall suburbia, and the kids, well, they’re naughty and nice in just the right ways. Young readers are bound to identify with these injustices of childhood and also the warmth within a caring family.