By 1934, Knowlden was seen as one of the few child actors to have established themself in a competitive industry. She was one of three actresses to portray Jessie Pullman (at age eight) in the 1934 Universal Pictures film "Imitation of Life". Over 100 children had auditioned for the part that she ultimately got. The film, based on Fannie Hurst's 1933 novel of the same name, dealt with the topic of passing (a theme that would again be explored in a film that she appeared in a couple of years later, "Show Boat"). She played Claudette Colbert's character's daughter as a child. It was nominated for an Academy Award for Best Picture at the 7th Academy Awards the next year. In 2005, the film was selected for preservation in the United States National Film Registry for being deemed "culturally, historically, or aesthetically significant".