John Key says his government is committed to reduce child poverty but says he will not sign up to the Children's Commissioner's call to cut child poverty rates by 10 percent by the end of next year.

Cut the 150,000 children living in poverty by 10 per cent by the end of next year?

It's a target the new Children's Commissioner Judge Andrew Becroft wants the Government to back but Prime Minister John Key won't put that number on it.

Key told RNZ on Monday that he wasn't "rejecting" Becroft - someone the Prime Minister says is doing a good job and was appointed for his skill set - but disputes that a number and a target can be put on child poverty.

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"We're very focused on reducing that number. We don't have one agreed measure...let's accept (Becroft's) measure then my point would simply be that I can't tell you today exactly what it would take to get a 5 or 10 per cent reduction," Key said.

"My point is simply...it's difficult to just have one measure."

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MARTIN DE RUYTER Prime Minister John Key won't sign up to a target of reducing child poverty by 10 per cent.

Key told media on Monday that having "one single measure of poverty" wasn't a very good way to look at the issue.

"The advice I get is that there are a number of different measures, they don't always cross over perfectly. So rather than spending time worrying about that, the Government's focusing attention on the kids themselves, rather than a particular measure."

LAWRENCE SMITH/FAIRFAX NZ Children's Commissioner Andrew Becroft wants cross-party consensus on measuring child poverty and a target for reducing it.

The Government isn't a stranger to targets - their Better Public Service targets are extensive in every area from NCEA pass rates for education to cutting reoffending in Corrections and the latest goal is to make New Zealand predator-free by 2050.

But Key says getting rid of rats, stoats and possums is a lot simpler than targeting children in need.

"It's more binary in terms of whether there's a rat, a stoat or a possum there or whether there isn't because you can understand that whereas all I'm simply saying to you, is look, it sounds airy-fairy but it's the advice we get that there are a range of different ways of measuring poverty."

Becroft left his job as Principal Youth Court Judge to take over as Children's Commissioner from Dr Russell Wills in July.

In an interview on The Nation on Saturday Becroft identified a simple system for adopting a target for reducing child poverty.

He wants to use the material deprivation index that has 17 indicators and when a child meets at least six they're considered to be suffering severe hardship.

Key knows the system well but says there's a "circular argument at work" and the "view from officials is that it's a complicated area and there are many particular measures you can use".

He told RNZ the number the Government typically relies on is that 60,000 to 100,000 children suffer "pronounced levels of deprivation".

"It doesn't mean the other kids who might be struggling don't deserve help and support, they do. That's why we've delivered seven million breakfasts since we've been doing the programme with Fonterra and Sanitarium."

"Isn't it better to say there are significant factors where a child is in significant deprivation and does need help and they could be a factor. So let's take rheumatic fever, isn't it better for the Government to say rheumatic fever is an issue potentially prevalent with high levels of deprivation - let's worry about that rather than the individual measure of poverty," Key said.

"My much stronger preference is to worry about the individual children rather than saying the number is x or y. You can have that debate all you like but I don't think it achieves much," he told media on Tuesday.

The Opposition has been quick to slam Key's comments with Labour's Andrew Little calling him "cowardly" in his refusal to commit to a 10 per cent reduction.

Becroft wants a cross-party consensus on a target and a pledge from both National and Labour to work towards reducing the number of children in poverty regardless of who forms the next Government.

Little has accepted that challenge and is calling on Key to do the same.

"The level of child poverty in New Zealand is shocking and inexcusable."

"(Key) will promise to kill every rat, stoat and possum in the country but says a target for lifting kids out of poverty is too big an ask," Little said.

"Labour will work with any party that is committed to ending child poverty. We've got the ball rolling with a member's bill that locks into law child poverty measures and a management plan, and I have personally committed to ending child poverty.'

The Greens have backed up Labour's calls for a target saying it's "ridiculous" the Government has one for eliminating possums but "refuses to put the same amount of effort into reducing the number of Kiwi kids living in poverty".

Greens co-leader Metiria Turei said her party is open to working with all political parties to reduce child poverty in New Zealand and is urging Key to board the bus as well.

Key said political parties will always have their own response to an issue and when "people go to vote in the election campaign they'll make up their own mind about which political party has the right set of measures".

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