OPINION: Just in time for Christmas, Labour is about to open the Santa sack for families.

Beneficiaries and pensioners will also feel the love as Labour uses the traditional end of year Treasury update to re-launch spending it announced on the campaign trail.

Most voters can be forgiven for thinking they're only hearing about this for the first time.

Labour botched its handling of its big ticket families package on the campaign trail so badly National managed to convince most voters - even the big winners from Labour's package - that they would be the biggest losers.

Read more

​* Going, going, gone? National and its legacy

* Labour's top priorities and those who'll make it happen

* Grant Robertson's journey to his 'anchor'

After the first post-election poll showing Labour's honeymoon is over barely before it began, Finance Minister Grant Robertson won't want to blow it again.

The midnight oil has been burning in his Beehive office as Labour works on what is effectively a mini-budget. It's not just critical that Labour sells the families package as a real boost to family incomes - after nine years out of power it needs Treasury's tick to show the sums add up.

Low and middle income families could potentially pick up hundreds of dollars extra a week from a boost to working for families payments and $60 a week for families with babies and toddlers. By the time people come to pocket National's April 1 boost to the accommodation supplement Labour will claim that one too.

Most of the package won't kick in till July 1. But it is significant. According to Labour's previous calculations a family on $50,000 with a new born and 3-year-old is $131 a week better off with its package.

There's also a winter fuel payment for beneficiaries and superannuitants, delivering $450 a year to a single person and $700 to a couple or a person with dependent children. It might be tagged as help for your power bills, but in reality it's to spend how you like.

But Labour never got cut through with voters on the package because National did a better job of selling it as a raid on their $2b worth of tax cuts.

Labour's political headache is that it still needs to cancel those tax cuts. Parliament will go into urgency immediately following the budget to tidy that up.

National will run hard on the losers under Labour's package, notably people without children. It won round one of that argument on the campaign trail.

But that was then, this is now. National is finding out that being in Opposition now makes it harder to get heard. And Labour has the megaphone of being in Government.

Expect Robertson to use it.