Social Development Minister Paula Bennett says children who were abused under the care of Child, Youth and Family are now safe.
Ms Bennett revealed on Tuesday a report she had commissioned shows 71 children were abused while in the agency's care in the year to June 2011 - 30 of them by their caregivers.
However, she has stopped short of ordering a review of the cases.
Ms Bennett told Parliament that collecting that data would require an overhaul of the IT system at CYF.
Acting CYF chief social worker Nova Salomen says the department is doing the best it can with the information available on children in its care.
Shetold Morning Report checks are in place to ensure children and caregivers are monitored, and she believes the department is doing the best it can with that information.
Jigsaw wants centralised monitoring
Child protection group Jigsaw says it is worrying that CYF does not have a centralised monitoring system.
Chief executive Sally Christie says many children in care are already vulnerable and distressed so their safety is absolutely paramount.
As well as better monitoring, she says a far more extensive support framework for caregivers, social workers and children themselves is needed.
Ms Christie says simply having social workers visiting homes every so often is not enough to ensure child safety.