A statement from the boy and girl, who cannot be named, was tendered to the ACT Supreme Court on Thursday as the arsonist faced a sentence hearing over their July 2019 attempted murders.

The primary school-aged victims told Justice David Mossop that when their single mother set fire to their suburban Tuggeranong home, they were scared but "mummy said to be quiet and stay in bed".

"After the fire it was bad that we were in hospital and we got needles," the siblings said in their statement.

"What has happened makes us very sad and angry.

"It made our family look bad. Mummy gave up on us being a family."

The children said they had lost all their clothes, toys and school awards in the terrible blaze.

They also told the judge that their mother used to "shout and scream" at them before the fire.

Of their new housing arrangements, they said: "We love our daddy and like living with him."

The 48-year-old mother, who worked for decades in the public service, is set to learn on Friday how long she will spend behind bars over her failed murder-suicide attempt.

Her former husband on Thursday implored Justice Mossop to impose a lengthy custodial sentence for the act of "true evil".

"I beg the court to think about the seriousness of this act, about a mother who was willing to kill her own children," the man said.

"I ask that she be suitably punished and incarcerated long enough so that my children can grow up without being put in danger physically, mentally and emotionally by the woman that was meant to keep them the safest."

The man also spoke of his initial disbelief that anyone would want to hurt his children, let alone their own mother.

"I was later told that it was due to her immense anger towards me," he said.

"It made her want to hurt her own children to get revenge on me for the breakup of our marriage that she instigated.

"I have been left to comfort two small children and try to explain to them why their own mother has done something so horrific that will scar them for the rest of their life."

Crown prosecutor Anthony Williamson told the court that the blaze had brought the victims "perilously close to death", which would have been only minutes away had firefighters not rescued them.

He said the offending involved a "deliberate, persistent and sustained endeavour" in which the children's mother had disconnected the smoke alarms in their home before setting the place alight.

It was particularly "horrendous", Mr Williamson said, that the woman had told her "utterly defenceless" children to stay where they were as a neighbour banged on a window in an effort to help.

To make matters worse, Mr Williamson claimed, the offender had not demonstrated any genuine remorse.

The woman's barrister, Steven Whybrow, strongly disagreed with that and said the 48-year-old felt "despair and horror" at nearly having taken her children's lives.

He sought to place the offending in context, saying this was not a case of someone trying to take revenge on a former partner.

Rather, Mr Whybrow said, a woman with a "longstanding and clear devotion to those children" had acted irrationally while "at her wit's end" after tumultuous divorce proceedings.

She had believed she would lose her house and thought her children would suffer more if they went to live with their father than if they died in a fire, the barrister told the court.

"It's not something that just happened because she's a horrible person, if I can put it that way," Mr Whybrow said.

Mr Whybrow said the woman's remorse was clear in her guilty pleas and character references, including one from a prison reverend who believed after more than 70 meetings that the woman loved her children "more than anything in the world" and felt "deep sorrow".

"That is powerful evidence of her contrition and remorse," he said.