Sydney family in hospital after open fire

Three young children, their parents and a police officer have been treated in a Sydney hospital for breathing difficulties caused by an open coal fire lit in the room in which the family were sleeping.

Paramedics treated two of the children, six and 11, outside their Liverpool home in the early hours of Saturday morning but their younger sibling, aged one, was taken to Liverpool Hospital by their 41-year-old father.

"The children's mother, 34, was also conveyed to hospital where all five members of the family were treated for carbon monoxide poisoning," police said.

A police officer was also hospitalised with breathing difficulties.

The family had used an open coal fire to warm the room in which they were all sleeping.

"There was no ventilation in the room with the door and windows closed," police said.

"Police have joined with other emergency services to remind people that it is vital to ensure that there is sufficient ventilation in rooms where an open fire is burning."

Further information on the family is being sought from the hospital, but the officer is fine and has been discharged, a spokeswoman told AAP.