Instead, he descended into a decade-long life of "lies, deceit and manipulation" by subjecting his children, one at a time, to sexual abuse, court documents show.

Most of the offending involved about 30 instances of incest and other acts of indecency at home, including while he was massaging them as part of their bedtime routine.

He said "I'm going to rub everywhere I can see skin" to one girl, who in a later traumatic incident said she squeezed her hands so hard that her fingernails would dig into her palms to "distract myself from the pain".

"I would either pray or sing a song in my head...I did all I could to block everything out," she writes in her impact statement.

"I feel so exposed all the time. It is like I am walking around naked all the time."

The offender handed himself to police in early 2021 to admit to the series of crimes that spiralled further as the years dragged on.

He did so only after one of the children revealed that "daddy's been touching me" as she broke down in tears.

After being confronted about his long-running sexual treachery, he said: "It's true and I'm relieved it's out in the open".

During a police interview, he said the massages against one child "got progressively worse".

"Um, to the point where the massage wasn't even important and I was just deliberately touching her," he said.

The offender is described in another heart-wrenching impact statement as having "clearly perfected the act of molesting vulnerable young females, choosing to focus on one target at a time and moving onto the next target when he feels compromised".

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The survivors, however, have vowed to fight their demons and lean on each other to find more peace.

One said despite the "decade of deceit, manipulation and lies", they will rebuild.

"We are creating new boundaries and building new walls to protect as much of ourselves and each other as we can," she said.

"We are all doing our very best to move forward with our lives in hope that we eventually find some freedom from all of this."

Another said that while "we feel like someone has robbed our past decade from us, we will do all within our power to recover from this and to one day learn to thrive again".

"This has had an unspeakable and horrific impact on our family...Having said this, I choose to speak only words of life over our future," she said.

"Our agreed mandate as a family is 'and still we rise'."

The offender appeared in the ACT Supreme Court on Friday after pleading guilty to three counts of engaging in a sexual relationship with a child under his care and one of committing an act of indecency on a child.

In sentencing him, Justice David Mossop described the case as "an absolute tragedy" as the offender "left such a trail of misery in his wake".

The judge said that after the death of the offender's wife, he had a chance "to be a hero to his children" but squandered it.

"Nothing about this would've been easy, but without the offending, he could've been proud of his achievements," Justice Mossop said.

"Instead he committed gross betrayals of their trust and isolated himself from the family.

"The acquiescence of the victims was not achieved by violence or threats of violence but rather as a consequence of the exploitation of the trust associated with the parental relationships."

In describing his abuse that his barrister labelled as "repugnant and morally wrong", the offender attributed it with the trauma from his wife's death, saying he was reaching out through their children for her physical touch.

However, Justice Mossop said that explanation was difficult to accept and sentenced the offender to 13 years and three months' jail with a non-parole period of 8.5 years.

The jail term was backdated to January to account for the offender's 288 days in pre-sentence custody.

He will be registered as a sex offender and will be eligible for release in July 2029.

If you or someone you know is impacted by sexual abuse, help is available at ACT Child and Youth Protection Services (1300 556 729) and 1800RESPECT (1800 737 732).

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