But Ardern said today it was important faith-based institutions fell into the Royal Commission's scope.
"Today paves the way for us to confront a dark chapter of our national history by acknowledging what happened to people in state care, and in the care of faith-based institutions, and to learn the lessons for the future," Ardern said.
Asked whether Christian community Gloriavale would come under the remit of the inquiry, Satyanand said it would be.
And although not mentioned, the infamous Centrepoint commune near Albany which operated in the 1970s would also fall under the scope of the Royal Commission.
Centrepoint was opened by Bert Potter in 1977 and was shut down in 2000 after some leaders, including Potter, were convicted of sexual abuse and drugs crimes.
Satyanand said the inquiry would be the largest Royal Commission ever undertaken in New Zealand.
The scope of the inquiry will cover a period of 50 years – from 1950 to the end of 1999.
But Satyanand said it had the discretion to look at cases before and after that period.
The inquiry has a budget of $78.85 million over four years, which includes more than $15 million to help participants by providing counselling and related support.
Satyanand said the budget was prudent. "We are providing New Zealanders with a process of healing."
Ardern said the Government had scrutinised the cost heavily – but that was the cost of having "thousands of voices being heard".
She also said if the Royal Commission called for one, the Government would provide a formal apology to the survivors of abuse.
Ardern said she knew some of the survivors and was proud to have played "even the smallest part" in the inquiry.
The duration of the Royal Commission has also been extended to four years to reflect the wider scope, Ardern said.
The Inquiry will be able to begin hearing evidence from January 2019.
A final report containing the Royal Commission's findings and recommendations will be submitted to the Governor-General in January 2023.