This child star of the 1940s was best known for her natural, emotional style and her startling facility for tears. As Maxine O'Brien (her birth name), she first appeared in a civil defense film starring James Cagney, then in a bit in "Babes on Broadway" (both 1941). Sensing her potential, MGM signed her, changed her first name to Margaret and starred her in the tour de force "Journey for Margaret" (1942), as a terrified London war orphan who "adopts" reporter Robert Young. It was an adult, intelligent and slightly scary performance which made her an overnight star. She was loaned out to Fox for "Jane Eyre" (1944). O'Brien's next big showcase came with "Meet Me in St. Louis" (1944). As Tootie Smith, the feisty but fragile little sister of Judy Garland, she was a bright point in a very good film, especially in her musical numbers with Garland and during a Halloween sequence in which she confronts a grouchy neighbor. For her performance, she was awarded a special juvenile Oscar. Her next two features, "Music for Millions" (1944) and the drama "Our Vines Have Tender Grapes" (1945) were also impressive. Two good roles came her way in 1949, as the tragic Beth in a remake of "Little Women" and as Mary Lennox in "The Secret Garden."