A mother cleared of any involvement in the death of her sons at the weekend remains in hospital in a stable condition.
Vanessa Robinson, 29, had been arrested after her sons were found in their Mooroopna home on Sunday night, but was ruled out as a suspect after tests were carried out on gas appliances at the house on Wednesday.
A spokeswoman for St Vincent's in Melbourne said Ms Robinson remains in a stable condition in hospital, where she was airlifted on Sunday after also falling ill.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
The testing by Energy Safe Victoria inspectors was ordered after police received information from the Coroner's Court following autopsies on the seven and nine-year-old boys, Tyler and Chase Robinson.
Homicide squad Detective Inspector Bernie Edwards said on Wednesday that their mother also appeared to have been affected by the gas.
Ms Robinson's condition began to deteriorate at Shepparton Police Station after she was taken into custody and she was flown to Melbourne on Monday in a serious but stable condition.
"It's believed that because she's an adult it hasn't affected her as quickly as it has affected the two little boys," Det Insp Edwards told reporters.
"We are fairly confident it's gas related. It was possibly over a number of days."
He defended police's decision to arrest Ms Robinson.
"The mother was the only one present with the children when they were found deceased," he said.
"It's common practice that that person is spoken to so we get to the bottom of the matter."
He said Ms Robinson and her former husband Scott Robinson, who separated several years ago, were informed of the developments on Wednesday.
Ms Robinson was "fairly devastated, as you would be", Det Insp Edwards said, but her physical condition was improving.
Further testing is still to be conducted as part of the investigation and police are also awaiting the outcome of toxicology reports.
