Answer by taking a quote from the following article:

Stanley Donen ( DAWN-@n; born April 13, 1924) is an American film director and choreographer whose most celebrated works are Singin' in the Rain and On the Town, both of which he co-directed with actor and dancer Gene Kelly. Other noteworthy films include Royal Wedding, Seven Brides for Seven Brothers, Funny Face, Indiscreet, Damn Yankees!, Charade, and Two for the Road. He began his career in the chorus line on Broadway for director George Abbott, where he befriended Kelly.

Stanley Donen was born in Columbia, South Carolina to Mordecai Moses Donen, a dress-shop manager, and Helen (Cohen), the daughter of a jewelry salesman. His younger sister Carla Donen Davis was born in August 1937. Although born to Jewish parents, he became an atheist in his youth. Donen described his childhood as lonely and unhappy as one of the few Jews in Columbia, and he was occasionally bullied by anti-semitic classmates at school. To help cope with his isolation, he spent much of his youth in local movie theaters and was especially fond of Westerns, comedies and thrillers. The film that had the strongest impact on him was the 1933 Fred Astaire and Ginger Rogers musical Flying Down to Rio. Donen said that he "must have seen the picture thirty or forty times. I was transported into some sort of fantasy world where everything seemed to be happy, comfortable, easy and supported. A sense of well-being filled me." He shot and screened home movies with an 8 mm camera and projector that his father bought for him.  Inspired by Astaire, Donen took dance lessons in Columbia and performed at the local Town Theater. His family often traveled to New York City during summer vacations where he saw Broadway musicals and took further dance lessons. One of his early instructors in New York was Ned Wayburn, who had taught eleven-year-old Astaire in 1910. After graduating from high school at sixteen, Donen attended the University of South Carolina for one summer semester, studying psychology. Encouraged by his mother, he moved to New York City to pursue dancing on stage in the fall of 1940. After two auditions he was cast as a chorus dancer in the original Broadway production of Rodgers and Hart's Pal Joey, directed by the legendary George Abbott. The titular Pal Joey was played by the young up-and-comer Gene Kelly, who became a Broadway star in the role.  Abbott cast Donen in the chorus of his next Broadway show Best Foot Forward. He became the show's assistant stage manager, and Kelly asked him to be his assistant choreographer. Eventually Donen was fired from Best Foot Forward, but in 1942 was the stage manager and assistant choreographer for Abbott's next show Beat the Band. In 1946, Donen briefly returned to Broadway to help choreograph dance numbers for Call Me Mister.

Was the only child of his parent ?
His younger sister Carla Donen Davis was born in August 1937.