A sprightly little serving of sibling rivalry, newborn-division--with a somewhat too facile conclusion: big-sister Lucy stops acting up and accepts baby Chuckie when the first word he says is her name. But the text is bona fide tongue-in-cheek storytelling on a child's level: ""Once there was a little girl named Lucy. . . . She said 'Please' and 'Thank you' and smiled when people said, 'Oooh, aaah, isn't she cute?'"" The light-fingered cartoons give a giggly cast to her subsequent mischief. Her ""ooohing"" and ""aaahing"" parents are figures of fun too (not objects of hostility). And Chuckie's perverse refusal to squall, no matter how much Lucy torments him, takes the sting out of her meanness. It's a safe and sunny way, altogether, for children to face up to their own resentments--so the specific reason why Lucy at last comes round matters much less than it would in an outright psychodrama.