Francesca Goodby saw her 28-year-old mother Kay in labour when she recalled an episode of the medical drama which saw a woman giving birth.
While her father was downstairs calling emergency services, Francesca was in the bathroom helping her mother through the childbirth, reports SWNS.
Roisin, weighing 6lbs 8oz, was born after 12 minutes of pushing.
Kay said afterwards: "I was so impressed with Francesca. She was remarkably cool and collected for a 6-year-old.
"She had gone to bed but woke up when I started screaming.
"She was keeping me calm and telling me where to put my hands and telling me to keep breathing... I was really surprised that she knew what to do and was so calm."
Francesca said: "I didn't want the cord to be wrapped around her neck, because she might have died, and I held her when she was born to keep her safe.
"I don't know how I knew about it, but I do watch Casualty and like it a lot."
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