PreS-Gr 2 Little sisters are a mixed blessing, according to this young narrator. But the last straw is when she decides that his turtle needs more exercise and turns it loose in a pond. The boy fantasizes about all sorts of ways to punish his sister. He punches his pillow and screams until he feels better. Finally, he is ready to make friends with her again, and off they go hand-in-hand to buy a hamster for each of them. Wilhelm's simply told story will strike a chord of understanding among preschoolers who have siblings. The watercolor illustrations, unframed on broad white pages with a few words, are expressive in their simplicity, helping to convey the message of forgive and forget. This is a pleasant addition to the sibling rivalry list, presenting a slightly different aspect of the subject than Martha Alexander's I'll Be the Horse If You Play with Me (1980) and Marty McGee's Space Lab, No Girls Allowed (1981, both Dial), Janice Udry's Thump and Plunk (Harper, 1981), and Elaine Edelman's I Love My Baby Sister : Most of the Time (Lothrop, 1985). Virginia Opocensky, Lincoln City Libraries, Nebr.