Terban has acted in local community theater plays to raise money for charitable causes. He has also had small parts in movies directed by Woody Allen. For many summers he directed plays at Cejwin, a summer camp in the Catskill Mountains north of New York City. He has paid "Meet the Author" visits to and given presentations about English language arts skills and humor in children's books at schools, colleges, and educational conferences all over the United States, South America, Europe, Israel, and Japan. Marvin and his wife live in New York City across from Central Park. They have two children and two grandchildren. Their grandchildren have two pet dogs and two pet pigs.