Sunset is our cat,"" begins Mrs. Stevens, and you believe her because from beginning to end the record of the birth of Sunset's kittens is precise, complete and tenderly respectful. Thanks to an unsurpassed sequence of photos (taken by her husband) and the informative, sensitive text. The shots of Sunset watching the first kitten slip out from under her tail, then changing focus, of the newborn kitten itself, still wet, still enclosed in its sac, immobilize a dramatic moment; the whole--Sunset eating the sac, cleaning and drying the kitten, poised for the birth of another, finally feeding all four--shares with children generally an event some never have a chance to see. Actually, it shows them and tells them more than they're likely to find out by themselves, plus reminding them that ""birth was both an end and a beginning for you too."" Happy birthday, Sunset's kittens. . . seen playing later on the last page.