The day after Darcey-Helen Conley was born her mother disappeared from the hospital for hours.
Kerri-Ann Conley's unexplained absences from the maternity ward were repeated when sister Chloe-Ann was born, a court has been told.
Within a few years the girls were dead after being left for nine hours in their mother's car where temperatures reached more than 50C.
An inquest into the deaths from hyperthermia of Darcey-Helen, aged two, and one-year-old Chloe-Ann on November 23, 2019 is set to be held in 2024, the Coroners Court sitting in Brisbane was told on Monday.
Conley was sentenced to nine years behind bars in February after pleading guilty to manslaughter.
CCTV cameras show Conley parking at her Waterford West home, south of Brisbane, at 4.05am, leaving the girls in the black Mazda wagon, counsel assisting Simon Hamlyn-Harris said.
At 1.16pm the footage shows Conley finding the girls unresponsive in their car seats.
Police recorded temperatures of over 50C inside the car.
Investigations found Conley was a heavy, regular user of methylamphetamine, with her behaviour putting the girls at significant risk of harm, Mr Hamlyn-Harris said.
They were often left in the car if asleep when Conley arrived home, people would access drugs at the house at all hours and the girls were regularly in the car at night while she engaged in drug-related activities.
She also had a habit of leaving the children with whoever might be at the house, saying she was going to get cigarettes but would be gone for a considerable time, Mr Hamlyn-Harris said.
Hospital staff raised concerns with Child Safety officers when Conley was absent from the maternity ward for long periods from the day after Darcey-Helen was born in May 2017.
"There were also concerns about her having to be prompted to feed the baby or to change her nappy," Mr Hamlyn-Harris added.
Darcey-Helen was removed from her mother's care in November 2017 after an anonymous caller reported her daily ice use.
But the child was returned about a month later when Conley agreed to receive support including from Uniting Care.
When Chloe-Ann was born in October 2018 Logan Hospital staff raised concerns with their child protection unit.
"They noted that during (Conley's) admission on the maternity ward, there were multiple occasions when she was absent from the ward for extended periods of time, leaving her baby unattended."
Child Safety officers were sceptical about the reliability of a report about Conley's drug use and the motivation of the reporter leading to a decision in November 2019 that the threshold for reporting a notification under the child protection law had not been met.
The appropriateness of that decision will be a central issue at the inquest as the girls died 11 days later.
State Coroner Terry Ryan will investigate what could have been done differently, and look at better practices to avoid something similar from occurring again.
The inquest will also consider information sharing by police with Child Safety and hear from a psychiatrist about drug usage and parenting.
A five-day inquest hearing is set to be held in Brisbane from April 29.
