Cummings was born in Joplin in 1910 and grew up there. His father was a doctor on the first staff of St. John's Hospital there, and Dr. Cummings also established a hospital in Webb City. Bob's mother was a Science of Mind minister. Bob learned to fly airplanes at a very young age, and when he was in high school, he earned money by charging residents of Joplin $5 to take them for airplane rides. When the government started licensing flight instructors, Cummings was issued Certificate #1, making him the first officially licensed flight instructor in the U.S. After high school graduation at Joplin, Cummings briefly attended Drury College in Springfield before moving to Pittsburgh, Pennsylvania, and later to New York to pursue an acting career.