In 1936 Barthold married Ruth Grünwald, a dancer at the Metropolitan Opera who had been just one year in the United States. Ruth helped Barthold with his work. Later she left him. Although he had no children of his own, Barthold Fles wrote two books for kids: "Slavonic rhapsody: the life of Antonín Dvořák" (in 1948) and "East Germany" (in 1973). He also wrote many articles and introductions to story collections. He translated three books from German to English. One of these books, Bambi's Children by Felix Salten, was also a book for children.