As the Depression deepened, the family moved to a ranch in Wyoming. Dirt poor and struggling, they pawned everything of value. A friend lent the family $300, and against Peggy’s wishes they returned to Hollywood and put her back to work, now as a teenager in the talkies. From 1932 to 1938, she appeared in eight films as an anonymous extra or in small roles credited to Peggy Montgomery.

She hated it. “Fighting for $3 a day in the world of extras — it was dreadful,” Ms. Cary told The Wall Street Journal in 2012. “And it was also sort of shameful, because the people who were doing the extra work were the former silent stars, many of them that I knew, who were adults, and for them it was a very crushing blow. I thought of it as being a galley slave.”

The family resorted to food coupons from the Motion Picture Relief Fund. The Los Angeles School Board finally insisted that the girl attend classes, and she enrolled at Lawlor Professional School, which had flexible schedules for young actors, enabling her to continue working. Fellow students included Judy Garland and Mickey Rooney. Later, she went to Fairfax High School in Los Angeles.

After graduating, she eloped in 1938 with her first boyfriend, Gordon Ayres, a movie extra. They were divorced in 1948. She was a switchboard operator and a bookstore clerk, and then managed a gift shop in Santa Barbara. She told no one of her past, and took the name Diana Serra. In 1954, she married Bob Cary, an artist, and took his surname. He died in 2001. Her survivors include their son, Mark and a granddaughter.

The Carys settled in Cuernavaca, Mexico, where he painted and she became a freelance journalist, writing magazine articles. In 1970, they moved to La Jolla, part of San Diego, and she began a new career as a film historian. Her first book, “The Hollywood Posse” (1975), was a well-received account of stunt riders in film. Her second, “Hollywood’s Children” (1978), recounted the often troubling stories of child actors.

But it was the years of work on her memoir, “Whatever Happened to Baby Peggy? The Autobiography of Hollywood’s Pioneer Child Star” (1996), that proved therapeutic and redemptive. She re-examined her life in silent films, her parents’ conduct in frittering away her fortune, the studios’ harsh working conditions and the fates of child stars who, like her, were left impoverished, emotionally scarred and largely forgotten.