In Focus - Prime Minister John Key has suggested it's easier to count the number of stoats and possums than measure the number of children in poverty.

The Children's Commissioner, Judge Andrew Becroft, is urging the National and Labour Parties to work together to cut child poverty rates by 10 percent by the end of next year.

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.

Mr Key told RNZ presenter Guyon Espiner on Morning Report today that the government was committed to reducing the number of children in poverty but didn't want to put a figure on it.

Asked why the government could set goals to make the country predator-free but not measure the number of children in poverty, Mr Key said it was a complicated area, and the advice the government had been given was it was difficult to have one particular figure.

He said it was more binary in terms of whether there was a rat or stoat or possum there, whereas there were a range of different ways of measuring poverty.

It was better to focus on factors that contributed to deprivation rather than the 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?'"

Under the material deprivation measure proposed by Judge Becroft as the official benchmark, 149,000 children would be considered to be in hardship.

Green Party spokesperson on inequality Metiria Turei said Mr Key may be refusing to commit to clear measurements and a target to avoid admitting the extent of the problem.

"That makes him a deeply irresponsible prime minister and unfit for the role," said Ms Turei. "Child poverty is one of the major scourges that this country faces."

Labour Party leader Andrew Little said the material deprivation measure classified fewer children as being in poverty than the one Labour used - but 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 that a rich country like ours ought to be able to do something about."

Susan St John, a member of the Child Poverty Action Group, also wants an end to the long-running debate on how to measure child poverty.

"What Judge Becroft is saying is please can we move on and please can we aim to do something about what is a digusting and dreadful situation now."