During his 1940s stint writing for Timely Comics, Hart lived in New Haven, Connecticut and commuted to New York City with his scripts. At the time he was living with his first wife and their sons, Allan (d. May 31, 1999) and Lance. When Lance was 9 years old, in the early 1950s, the family moved to Orange, Connecticut, where they built a house near a veterinary clinic run by Hart's longtime friend Leon Whitney. Partly through this connection, Hart and his son Allan eventually became beagle breeders whose dogs included the bench champion Lynnlann's Button Up. Hart continued as a freelance writer, and combining his vocations by writing and editing nonfiction books for dog-owners. He became a dog-show judge and importer of German shepherds, and in 1960, with Charles Kaman, co-founded the nonprofit Fidelco Breeders Foundation to produce German shepherds of "true working dog temperament and utility."