The Prime Minister's hoping there will be cross-Parliament support for her child poverty reduction framework.

Jacinda Ardern will announce later this week her promised law change requiring all future Governments to set poverty reduction targets, and report on their progress on those in the Budget.

From then on, stats on child poverty are to be written into every Government Budget.

It's one of her last- first 100 day- promises, and she hopes there is a real buy-in by all parties.

"We've offered to brief opposition parties and I want to work very constructively.

"I think the way it will stand the test of time is if they agree with it from the outset."

Ardern said the poverty reduction framework will be written into the Public Finance Act - a rule-book a Government cannot afford to breach.

"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 well-being issues, every time we write a budget."

However, the National Party won't be giving the government an easy ride.

"There was an assumption that because there was a new government, we were there to make their job easier to do," National Party leader Bill English said on Monday.

"But if they're doing things we think are bad for New Zealand, then we will make it harder for them - and we've got more seats than Labour and NZ First put together."

He said filibustering - the tactic of delaying legislation by dragging out debates - was part of "the standard toolkit of opposition".

English isn't happy about the way the government has gone about cross-party co-operation so far.

It's going to need National's support to get the new Trans-Pacific Partnership through parliament because the Greens aren't going to vote for it.

That support will be there when it's needed, but Mr English doesn't like the way it's being taken for granted.

"They've been attacking National's record on the TPP, which isn't the best way to create a constructive relationship," he said.

"The government has got a bit to learn about working with other parties."

ACT leader David Seymour has said he is unlikely to support it.

"The only way I'd support this as ACT is if Winston Peters and Jacinda Ardern take some remedial courses in economics so they can learn how to actually measure poverty, because the kids are too important for the kinds of political games these guys are trying to pull."

- with content from NZ Newswire