One of the twins found unconscious in the backyard pool of a home in Sydney's north-west last week has died, as the other continues fighting for life.
Emergency services were called to reports that two unconscious children had been pulled from a pool in Charbel Place, Kellyville Ridge just after 7pm on Tuesday night.
The girl and boy, aged 23 months, were treated by paramedics at the scene and then taken to Westmead Children's Hospital.
The young girl remained in a critical condition until she died earlier today.
Her twin brother continues to undergo treatment and remains in a critical condition.
A brief will now be prepared for the information of the NSW Coroner.
Last week, a next door neighbour told 9NEWS she heard the mother screaming and rushed to help the family, performing CPR on the young children with her husband as their parents performed mouth-to-mouth.
"I didn't think about it, we were just straight over there and straight into it," Michelle Skevington said.
"We just kept going and going until paramedics arrived."
It's believed the twins were out of the sight of their parents for a period of time, police said.
"Like any other accident it tears at your heart strings, these are normal babies that are toddling around and then the next thing they are on life support and in intensive care. It's horrible for families," Andrea Christoff from Westmead Children's Hospital said.
Thirty-five children have been treated this year for injuries sustained during misadventures involving water.
