Munro grew up on the road with her father, often appearing with him on stage. Her mother died when Janet was seven and she was brought up by her father at first. She later recalled "during the war he was head of entertainment for the RAF and I went along with him wherever he happened to be. We entertained the troops. I wore kilts and sang. My voice was even smaller than I was but the boys didn't seem to mind – I was a bit of baggage from home."