National leader Bill English says the Government is not looking at the entire picture when it comes to poverty.
Details of Jacinda Ardern's child poverty reduction law, a key election promise, will be released on Tuesday afternoon.
It's one of a handful of changes her Government will push through this week when Parliament resumes, with the aim of lifting 100,000 kids from hardship in the next three years.
But National leader Bill English says the new Government's approach "makes no sense" and only focuses on half the picture.
"We were proposing increasing some of the lowest incomes. The Government's gone ahead and done that and added a bit more to it.
"But the other half of the story with poverty is the social dysfunction that traps people in it for a long time - long-term welfare dependency, child abuse, often ill-health, disability.
"The targets that were in place - the Government's abolished."
The Bill is reportedly "very, very complex". Government departments will have to meet certain targets to reduce child poverty, and whether they succeed or not will be reported by the Treasury.
The Prime Minister says this will ensure that child poverty remains a priority across all departments.
"The fact that we're going to have to report on how we're doing at the Budget will shape the way that we look at child-wellbeing issues every time we write a Budget," Ms Ardern said on Monday.
But Mr English says the Government doesn't have any means to measure its progress.
"We think the Government should be accountable for spending our money to change lives.
"If this Government's decided not to hold itself to account - and that's what it looks like at the moment - then as the National opposition we've decided we'll collect the information so that you can see whether they are making a difference for thousands of New Zealanders who do need a big difference made to their lives."
Mr English says on Wednesday the National Party will lay out its own plan of action for the next three years - and hinted at what can be expected.
"We'll just be laying out how we're going to go about our job which is essentially to support those things the Government does that are good for New Zealand and to go after them and try and stop them doing really dumb things that are bad for New Zealand."
But UNICEF chief executive Vivien Maidaborn told The AM Show she's encouraged by the Government's approach.
"You have to say that it's way better than any Government has done in the last two decades.
"This has put a completely new stake in the ground - for not just this Government, but Governments going forward - that they say what their definition is and they hold themselves accountable."