Parents battling to get their children back from state foster care are being stymied by two-month delays to get hold of their official files, a lobby group says.

The Ministry of Social Development says it is still processing 1177 requests for current and historic client files under the Official Information Act, and estimates that responses to current cases "will be provided within two months".

Lobby group Positive Answers Needed In Crisis (Panic), which supports families dealing with the ministry's Child, Youth and Family Service (CYF), says the delay means many cases are decided in the meantime on information that turns out to be incorrect.

"In a number of cases where files are received, a number of errors in social workers' file notes are seen," said Panic co-founder Angie Rogerson. "Some could easily be proved as incorrect and could result in a very different court or family group conference outcome."

CYF has struggled with an almost fivefold increase in notifications of suspected child abuse and neglect over the past decade, from 27,500 in 2001-02 to 152,800 in 2011-12, as a result of increased public awareness and a policy change by police who now notify CYF of all cases where children live in a home where a domestic violence incident occurs.

Many are multiple calls about the same families, and many require no further action. But even notifications of distinct individuals requiring further action have more than doubled, from 21,100 to 48,500.

Data for the past five years provided to Labour MP Jacinda Ardern shows that CYF staff numbers have also increased, but at a much slower rate, from 2741 fulltime-equivalents in June 2008 to 2938 in March this year.

After excluding specialist, contact centre and national office staff, the workload has increased from 16.6 notifications of distinct individuals requiring further action for every fulltime-equivalent local CYF worker in 2007-08 to 24.2 in the past year.

The northern (Auckland/Northland) region had a much higher notification workload than the agency's other three regions in 2008, and has gained 84 extra local staff since then.

The ministry's manager of ministerial and executive services, John Wilson, said CYF received an average of 145 requests for client files a week in the year to June, and this had increased recently to average 165 new requests a week.

"On average, a response will contain 400 pages of case file material. Case files will contain personal and sensitive information, and require careful attention when forming a response," he said.

"Given that, we estimate a response to a request for a current case file will be provided within two months.

"If it is necessary to extend the time frame beyond the 20 working days [under the terms of the Official Information Act] the requester will be advised of the reasons for this.

"If people require specific information within a file for a specific purpose, or if a request is determined to be urgent, we can work with requesters to speed up their request."

By Simon Collins Email Simon