THE GIRL WHO CHANGED THE WORLD

It's war—the younger sibs, fed to the teeth with the hazing they've gotten for as long as they can remember, organize a rebellion led by Violet Sparks, whose particularly obnoxious brother Simon (first seen swatting a juicy fly into Violet's hair while she's performing at a piano recital) becomes hostage and target for revenge: trapped at the Youngers hideout, he's read a list of gruesome deaths before being subjected to several stages of ``Death by Tickling.'' Meanwhile, the Youngers have learned to get the Olders' goats by ignoring their verbal abuse and issuing some of their own, as well as by giving them enough slapstick comeuppances to keep the farcical story moving and prod the Olders toward reform. The parents, sensibly, decide to butt out; and the broadly sketched antics are neatly rounded out as each sib realizes a basic bond with an erstwhile nemesis. Bringing a deft, light touch to her first children's novel, humorist- screenwriter Ephron focuses on dialogue and action that read almost like a script. Her five pairs of sibs are amusingly varied, with a middle child, an only child, and a trio of animals thrown in. Thank goodness sibling rivalry isn't always this bad (nor is it so easily dispelled); but the Youngers' feisty cure makes an entertaining romp. (Fiction. 8-11)