NEVER BABYSIT THE HIPPOPOTAMUSES!

What if you were a small boy—say, a rather slender-looking eight-year-old—babysitting a couple of hippos who behaved like rambunctious children? That's the slight idea here, but it's developed into a book that will amuse kids with its exaggerations of their own behavior, plus some incongruities special to hippos (``Don't play leapfrog with them, they can be hard to jump over. Don't play horsey either. They always want you to be the horsey''). From a game of hide-and-seek to bath-splashing, book- reading, and tucking in (more than once), the proceedings are considerably enhanced by Carter's free-form watercolors, where the hippos—who are a luscious shade of green—cavort in a house in which every normally straight line (door-frame, banister, drawer) is as energetically warped as a twanging rubber band. (Picture book. 4-8)