Malcolm Turnbull has signalled he's open to further changes and a fresh overhaul of family benefits if they're found to be unfair.
The government on Wednesday introduced what it described as "fairer and better" changes to family payments, clearing the way for a yet-to-be-revealed childcare package.
The package replaces a series of tougher measures outlined in former treasurer Joe Hockey's 2014/15 budget and blocked by the Senate.
Family Tax Benefit Part B will now cut off when a family's youngest child turns 13, instead of age six under the original unpopular plan.
Those receiving Family Tax Benefit Part A will get an extra $10 a fortnight for each child in the family aged up to 19 from July 1, 2018.
But supplements to both Part A and B - around $726 and $354 a year - will be phased out over the next three years.
Labor used question time on Wednesday to quiz the prime minister on how many families would be better and worse off.
Opposition families spokeswoman Jenny Macklin was more specific, asking Mr Turnbull to confirm that a grandparent carer with a 15-year-old in their care would be about $2500 a year worse off.
Mr Turnbull said given that the social security budget was $154 billion a year, changes were needed to get payments under control.
"We have to be careful and systematic and, if the honourable member has specific challenges about a particular part of the policy, then she should raise them and they will be taken into account," he said.
"But we shouldn't be trying to play an old-fashioned gotcha game ... let's focus on substantive policy just for a change."
Social Services Minister Christian Porter said he was happy to have a "cup of tea" with Ms Macklin to talk about the impact on grandparents who are carers.
Single parent families with a youngest child aged 13 to 16 will see their $2737.50 annual payments drop to $1000.10.
"What we do not want to see is hard-working Australian families ripped off by out-of-touch Liberals," Ms Macklin said.
The government says the savings will largely be "in the same ball park" as the $3.7 billion first flagged and set to fund its childcare package.
Talks are under way with Senate crossbenchers to get the revised package through the upper house.
Independent senator Glenn Lazarus said he was encouraged to see the government listening and compromising but was still considering the changes.
Liberal Democrats senator David Leyonhjelm plans to support the government but is less supportive of using the savings for childcare.
Greens families spokeswoman Rachel Siewert said the cuts disproportionately target the most vulnerable families, especially single parents.
The Australian Council for Social Service said the package did not properly address poverty, which affected about 600,000 children, or incentives to work.
