When Nancy was around sixteen years old, she became pregnant. Due to the stigma surrounding unwed teenage mothers in the 1930s, she told everyone that her son, Jamie, was her brother. In January 1941, Jamie was killed in an air raid near Limehouse Green station, but Chula nanogenes partially revived him, however because they had never been in contact with a human before they thought the gas mask he was wearing was part of his body and they revived him as the Empty Child. The virus spread to other humans at Albion Hospital and began "correcting" and "fixing" them to look like what they thought a human looked like.
Because of her son's death, Nancy took it upon herself to look after children who had been evacuated during the London Blitz, but had returned as strays. She stole food from families as they hid in air-raid shelters. Nancy met the Ninth Doctor during one of these meals and warned him about Jamie. She suggested he ask Dr Constantine at Albion Hospital for information. (TV: The Empty Child)
Nancy didn't believe that the Allied Forced would win the war. When Rose Tyler told her that she was born in London, "in like, fifty years time," Nancy was surprised because she believed future Londoners will be German.
When Nancy told the Child, who kept asking for his mummy, that she was his mummy, the nanogenes reprogrammed themselves, restoring Jamie and the other infected humans to normal. (TV: The Doctor Dances)