Child Youth and Family is reviewing the cases of more than 200 children thought to have been subjected to continued abuse and neglect despite repeated warnings to social workers.
Children's Commissioner Dr Russell Wills said the children had been referred to CYF more than 20 times each and the notifications could include everything from serious violence to children repeatedly turning up to school hungry.
"I wish it was none but you're going to have kids who have repeat notifications," he said.
The review was sparked by District Court Judge Dale Clarkson's criticism of CYF in December after social workers failed to respond to 21 warnings relating to four siblings who were abused and neglected by their father, a convicted child rapist, and their mother, who left them alone in a South Auckland mall carpark.
Judge Clarkson was so alarmed at CYF's "disappointing lack of protection" that she referred the case to Dr Wills. His review of a report by CYF chief social worker Paul Nixon into that case has been completed, but Dr Wills said CYF was doing a second review that would focus on the 200 children referred to CYF more than 20 times in the past 10 years.
"That's a big deal, and it suggests that someone hasn't put the picture together." He said the review would take some time and he was confident the findings would be robust.
Labour's social development spokeswoman Jacinda Ardern said it was not clear if the 200 cases included substantiated abuse cases. "But I just don't think it's acceptable that we're leaving any vulnerable children in a situation of abuse when CYF knows about it," she said.
Social Development Minister Paula Bennett said she understood CYF was reviewing the cases with 20 or more notifications to look into the decision-making and practice for complex cases with multiple notifications
"I welcome CYF taking an opportunity to take a step back, ask questions and find ways to improve practice and policy," she said.
CYF has refused to release its report into the case dealt with by Judge Clarkson but an executive summary found social workers were "overly optimistic" about the parents' abilities to change their violent behaviour.
CYF deputy chief executive Bernadine Mackenzie said the review found some staff did not perform.
"We have entered into a (human resources) process with three staff. A small number of others are having discussions with management around their work."
Dr Wills said the problem stemmed from a pattern of high staff turnover and huge workloads coupled with superficial assessments by individual social workers.
"A social worker should have sat down with a supervisor and gone through the whole history. They didn't, that was a mistake - it was a serious mistake - and the review acknowledges that."
Dr Wills said while it wasn't unusual for parents to lie, avoid social workers and move around the country, it was unusual for cases of that nature not to be reviewed by staff.
He said CYF's workload needed to be reduced and this could happen as police and health providers increasingly referred lower-level cases to community organisations.
According to CYF figures, the numbers of referrals have gone from 40,939 to 152,800 in nine years. Dr Wills attributed that in part to a change in social attitudes towards violence and campaigns such as the "It's not OK" anti-violence" campaign.
Mr Nixon said improvements had been made since the 2000s. "For the first time in over a decade Child Youth and Family is consistently delivering against every single commitment."