The number of Kiwi kids in poverty jumped by 60,000 in the recent global recession - twice as much as previously reported.
Revised figures show that children in homes with under 60 per cent of the median income after housing costs, usually cited as New Zealand's poverty line, leapt from 240,000 in 2007 to 300,000 in 2010, the highest since 2001.
The number has dropped back since then to 285,000, but this is still 20,000 more than the previously reported figure of 265,000.
The revisions, disclosed today, are mainly because the accommodation supplement was double-counted in all estimates of after-tax income reported by Statistics NZ, Treasury and the Social Development Ministry since 2009-10.
A joint statement by Treasury and Statistics NZ said the figures were produced jointly by the two agencies and "neither agency had an overview of the complete process to ensure the anomalies, once identified, were properly explained."
"Statistics NZ and the Treasury have changed their quality assurance and communications processes to ensure this problem doesn't happen again," they said.
As a proportion of all Kiwi children, the revised figures show that children in homes below the poverty line increased from 22 per cent in 2007 to 28 per cent in 2010, and have dropped back only slightly to 27 per cent - not 25 per cent as reported previously.
Children's Commissioner Dr Russell Wills said the figures were still too high.
"With 25 per cent it was already pretty important. At 27 per cent it's still important. Really the message is the same, and it's that child poverty is too common and we need to plan for it," he said.
He said there were signs that child poverty had dropped since the latest figures, which relate to 2012.
"I have been pleased to see that the number of children in benefit-dependent households has fallen. There are more parents in work," he said.
"For most, work is the best way out of poverty, and we clearly still have a long way to go on that."
Children in homes with under 60% of median income after housing costs
Source: Social Development Ministry