The Child Abuse Squad has been called in after a five-year-old girl found unconscious in her bed tested positive for methadone.
Hawkesbury duty officer Peter Jenkins said the girl's grandfather tried to wake her at Quakers Hill, in Sydney's west, around 1.30pm on Tuesday but she was non-response and having difficulty breathing.
The man called Triple-0 and began CPR on the little girl.
Vials of methadone were found at the house when emergency services arrived, Insp Jenkins.
"One examination (at hospital) has revealed the child had methadone in her urine," Insp Jenkins said.
The girl was airlifted to the Children's Hospital at Westmead.