Flavia Gág was a daughter of Anton Gág, the Minnesota painter and photographer, and the much younger sister of Wanda Gág. She attended local secondary schools before going on the study at Stetson University. She remained unmarried. Flavia Gág's children’s stories, which she illustrated herself, were published in various children’s magazines such as Child Life and, Jack and Jill. Her books included the collection of songs Sing a Song of Seasons (1936), Fourth Floor Menagerie (1955), and The Melon Patch Mystery (1964). She had begun a biography of her sister which remained unfinished when she died.