The girls had posed as a toddler claiming she was trapped at home with her unconscious mum.
They kept emergency services on the phone for 33 minutes as they spun their lies, which led to a huge search being launched on Monday for a girl called "Ellie".
The 'toddler' said her mother was 'Stacey Hall' and they lived in Leeds.
She said her mum had collapsed in the kitchen with a piece of toast in her hand, adding: "I've tried wiggling her about and shouting at her but she won't wake up."
Detectives were so worried that they put out a four-minute excerpt of the call nationwide in the hope that the public would help.
But four hours later they traced the emergency call - one you can make without a sim card - and found it was a hoax.
It led them to Bridlington, East Yorks - and the two girls on school holidays. No decision has been taken about charging them.
But senior officers said they had been 'spoken to' along with their parents. Social Services are also understood to have been called in.
Det Chief Insp Lisa Griffin said: "We are pleased we don't have a vulnerable girl out there with her mum collapsed beside her - although it is incredibly frustrating that this turned out to be a hoax."
How shocking! So entirely different from a toddler or baby inadvertently pushing 999!
More:Advice And Health
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