No longer confined to atmospheric fairy tales, stepparents can appreciate this brisk, informed guide which keeps the needs of the whole family in mind. The Rosenbaums, psychotherapists and stepparents, emphasize the context of each situation and consider the outlook of each of the principals. Basic advice: be flexible and don't expect gratitude. For those who've never parented before, they include a section on child development--adequate on the early years, too cursory on the middle years, commendable on adolescence. (Feminists take note: ""The gender-identity period is quite different for the sexes, and not just culturally either."") Their examples of problems encountered vary with each age group and reflect an understanding of the seesaw of feelings which adults and children experience. They comment on parental idealization and reunion fantasies, discipline procedures, and the necessity for communication--not the catchword but an ongoing process. Despite the intermittent use of jargon (hassles, guilt trips), they tend to write directly to the issue: of new brothers and sisters, ""Unless murder seems imminent, let the kids thrash out their own problems, as all peers must do."" Clear sights on a clouded phenomenon.