Whelan, the daughter of Mike and Karen Whelan, was born on 1 July 1992 in Singapore, where she lived until she was two years old. Her family then moved to Stockport, England. It was there that Whelan began gymnastics. She said: "At the age of six, after constantly cartwheeling around the house and Tesco, I persuaded my mum to take me to a gymnastic class. There, I was immediately spotted as a talent and began training at South Manchester Gymnastics Club with coach Helen Hall." A year later, when Whelan was seven, her family moved to the United States, where she trained at Flips Gymnastics Academy in Texas. In 2001, at the age of nine, she moved back to Stockport with her family and resumed training with Hall, this time at Vernon Park Gymnastics Club.