A straightforward fictional presentation of a common experience. Daddy telephones Hessie (who's about six) right after Sam is born, but she meets the baby for the first time when she arrives to spend her summer vacation with Dad and stepmother Molly. Sam isn't exactly what Hessie expected, but they are soon enjoying each other--in spite of such minor inconveniences as having to wait for him to wake before they can go to the beach. Boyd chooses realistic events that reveal common reactions and describes them with sympathy; her pen-and-wash illustrations employ flattened perspectives--as well as her own unique, archly sophisticated style--to cheerfully expressive effect. Useful but not exceptional, this could double as an easy reader.