A final report by the Independent Police Conduct Authority says the police handling of child abuse cases has been undesirable, unjustified and unfair to the victims.
An interim report released in May last year made 34 recommendations, which police have now acted upon.
The IPCA review was prompted by a situation in Wairarapa where, over two days in September 2006, officers closed 33 cases by either filing them incorrectly or wrongly deciding they had been solved.
The problem was only brought to the authority's attention in June 2009.
The review found that, though there were problems in other parts of New Zealand, Wairarapa was the worst. After some investigation, it was decided to broaden the scope of the inquiry to cover the whole country.
Detective Inspector Jim Gallagher is responsible for the child abuse team and accepts that things went badly wrong in Wairarapa.
"No district should ever fall into the state that the Wairarapa did in terms of their inability to respond to the demand for investigation of child abuse reports there, and also the fact that they were unsupported through the district as a district response to that situation."
Eighteen officers are being investigated over the treatment of child abuse files and five have so far been cleared of any misconduct.
Some 67 staff have gone through a more informal process about their job performance. Mr Gallagher says many of them will have been moved on to other work.
National child abuse prevention group Jigsaw says the final report into police failures to investigate cases is tragic reading.
Spokesperson Liz Kinley says the situation in Wairarapa was unfathomable and entirely indefensible, but what is heartening is that the report makes transparent all the tragic failings on behalf of children.
Concerns addressed, says IPCA head
The head of the Independent Police Conduct Authority says she is confident police have addressed the concerns it had about their handling of child abuse cases.
Justice Lowell Goddard says while the problems in Wairarapa were acute and high risk, generally there was not a national or widespread problem.
Justice Goddard says she is confident that the positive police response means the authority's concerns about systems failures and inconsistencies of investigation into child abuse have been addressed.
Police say they have implemented all the authority's recommendations and as a result the public can have confidence in their ability to deal with child abuse cases.