The terms of the upcoming Royal Commission on abuse in state care excludes institutions such as churches unless children were sent to them by the state.
Ardern has previously said that state care survivors did not want their cases "diluted" by the Royal Commission looking into abuse by the Church.
Ms Ardern told RNZ last month that distinction was made because the state had essentially been a parent in the past so needed to take responsibility.
"There is no doubt that there will be religious institutions who will be brought into the remit of this inquiry by virtue of the fact that children in state care may have in some form been sent there. This inquiry allows us to then look into both what occurred to that child via the state, the state's role in seeking to respond when that abuse was often raised and they didn't always respond to it but also what actually happened with those institutions too," she told RNZ.
The Royal Commission will focus on the victims, including any systemic bias based on race, gender or sexual orientation, but it will not compensate individual victims.
It will begin hearing victims' stories within six months, with the aim of reporting back by the end of the parliamentary term.
The inquiry is expected to cost $12 million in its first year. The draft terms of reference state that the inquiry will:
• Look at physical, sexual and emotional abuse and neglect.
• Look at bias against Maori but also based on gender or sexual orientation, and against those with disabilities or mental health issues.
• Consider the nature and extent of abuse, immediate and long-term impacts, the factors (including systemic factors) that contributed, and lessons to be learned.
• Cover a period of 1950 to 1999 - though this can be broadened
It will not consider individual compensation, but instead invites feedback on the Ministry of Social Development's historic claims process. It will also include a support mechanism for anyone that wants to lay a complaint with police.
State care includes child welfare and youth justice placements, as well as care in health, disability and special education facilities, such as psychiatric hospitals and residential care facilities, residential special schools and health camps.
It does not include prisons, former penal institutions, general hospital admissions or schools, unless the person was in state care at the same time.