Tolley said the abuse of children was abhorrent but successive governments had decided against a full inquiry.
"This service provide more in the way of help than an inquiry ever would, helping people access their old records, funding counselling sessions, and referring them to agencies for investigation."
She said that meant the Government had been able to deal with claims directly and quickly. "An inquiry would not resolve the claims of individuals or provide payments or offer personal apologies."
The Mana Party's Hone Harawira has also called for a Commission of Inquiry, and Fox acknowledged that.
Her fellow co-leader Te Ururoa Flavell said there was need to acknowledge that horrific and widespread sexual and physical abuse occurred.
"We will probably never know how widespread this abuse was and I suspect there are still some out there who are too traumatised to publicly acknowledge it.
"It's this lack of information that makes it imperative that we have this inquiry into the abuse of tamariki in institutional care."
Fox said the Children's Commissioners' State of Care report on that service was based on the experiences of more than 1,100 people who suffered abuse at the hands of the state and that was reason enough for full inquiry. She said that was needed to ensure such incidents never happened again.
Tolley said the new Vulnerable Childrens' Ministry was based on an expert advisory panel's study of that issue and she was confident it would never happen again. "Thankfully the era of borstals and 100,000 children in state care are long gone."
In February, the Human Rights Commission issued an open letter to Prime Minister Bill English, saying an inquiry was needed to acknowledge the abuse and harm done to children who were placed in state care in those decades and provide a platform for them to speak.
The Human Rights Commission says more than 100,000 New Zealanders were taken from their families and put into state institutions from the 1950s to the 1990s and many suffered physical, sexual and emotional abuse and neglect. That included disabled children taken from their families.
Indigenous Rights Commissioner Karen Johansen has said Maori children were more likely to be taken from their families - some institutions had reported 80-100 per cent of children were from more than Maori homes, and more than 40 per cent of prison inmates spent their childhood in state care.
