The Labour Party has accepted the Children's Commissioner's challenge to reduce child poverty rates by 10 percent by the end of next year.
Commissioner Andrew Becroft is urging National and Labour to work together to achieve the change.
Mr Becroft wants a material deprivation measure to be used as the official benchmark for child poverty, under which 149,000 children would be considered to be living in hardship.
The political arguments over just how many children were in poverty needed to stop and more action needed to be taken, Mr Becroft told TV show The Nation at the weekend.
Labour leader Andrew Little said, while that measure produced a much lower number than the one Labour currently used, the time for quibbling was over.
"It doesn't matter what the measure is - let's just have one.
"And then let's just work on reducing that level of poverty, because it's wrong, it denies future life opportunities and it's something a rich country like ours ought to be able to do something about," Mr Little said.
Prime Minister John Key said earlier it was too difficult to measure definitively the number of children in poverty, and so a target could not be set.
Mr Key told Morning Report that the government was committed to reducing child poverty but didn't want to put a particular figure on it.
It was better to focus on factors that contributed to deprivation rather than exact numbers, Mr Key said.
"Isn't it better for the government to say, 'Rheumatic fever's an issue, potentially prevalent with high levels of deprivation, and therefore let's focus on that', rather than worry too much about the individual measure of poverty?'"
Green Party co-leader Metiria Turei said it was inexplicable that Mr Key would not set a target, and described his refusal to commit to one as irresponsible.
"He may be refusing to set a target and clear measurements because he doesn't want to acknowledge the extent of the problem; that makes him a deeply irresponsible prime minister and unfit for the role," Mrs Turei said.
"Child poverty is one of the major scourges that this country faces."