What makes some documentaries valuable is the light they shed on subjects far outside our normal rounds of experience. But sometimes the most involving nonfiction films are those dealing with material quite close to home.
Proving this point, a quiet and compelling movie called ''Martha & Ethel'' has become one of the rare documentaries to go into regular theatrical release -- courtesy of Sony Pictures Classics, which is distributing the film after its well-received premiere at last year's Sundance Film Festival.
''Martha & Ethel'' focuses on a time-honored profession: that of the ''nanny'' who raises children when parents are reluctant or unable to do the job alone.
The movie's director, Jyll Johnstone, first conceived the project as a 20-minute study of the German-born nanny who raised her and four siblings over a 30-year period starting in the early 1940s. The film took on feature-length proportions when Barbara Ettinger became coproducer, bringing in the African-American nanny who played a central role in her household during the same period.
Although both are nannies in the classic sense of the term, Martha and Ethel prove to be very different as people and as professionals. Martha became a baby nurse in her native Germany, taking a comfortable job with a wealthy Jewish family. This position disqualified her for further employment when the Nazis came to power, so she moved to the United States and eventually settled into the Johnstone's home. As interviews with Martha and the now-grown family show, she was a disciplinarian who never questioned Old World notions that coolness, strictness, and sparsely granted affection are just what children need.
Ethel also left home in the '30s, trading her Southern sharecropper roots for a more exciting life in cities to the north. Her job with the Ettingers assumed new importance when the couple divorced, greatly increasing her responsibility for their six teenagers. Again, a series of on-camera interviews and shared recollections give fascinating glimpses into her personality, which appears to be exceptionally warm, caring, and outgoing.
If this double nanny-biography were all ''Martha & Ethel'' had to offer, it would be a likable but unmemorable movie. Lending extra resonance is the portrait it paints of the Johnstone and Ettinger families, and of the filmmakers who grew up within them. Both families hired a nanny by choice rather than necessity, and present-day interviews with the children indicate a lingering uneasiness with the distant parent-child relations that resulted.
Although the movie draws no definitive conclusions, it raises important questions about how to balance order and convenience with love and affection while raising children in a materialistic society. It also brings needed attention to the nanny profession itself, which is often taken too much for granted -- as are individual nannies, to the point where Sony's production notes for ''Martha & Ethel'' don't bother supplying last names for either of the women in its title.
The film might have been more revealing if it had been made by outsiders who could look at all these nannies, parents, and children with fresh and unprejudiced eyes; yet some of its appeal stems from the honesty and generosity shown by the filmmakers in sharing their experiences. Moviegoers who decry the sorry state of mainstream films should make a point of seeking out ''Martha & Ethel.''