The modelling, commissioned by Early Childhood Australia, says about 330,000 families will be worse off under the changes due to start in July 2017, compared to about 184,000 in the government's figures.

Education Minister Simon Birmingham told Fairfax Media the government had access to a different data set and its modelling could "absolutely be trusted".

The ANU figures also show only 708,400 families will be better off or experience no change, compared to the government's predicted 956,200.

The university modelling, done by associate professor Ben Phillips, also suggests families will be much harder hit by the new "activity test" (where parents will have to work at least eight hours a fortnight to qualify for subsidies), with more than 127,000affected compared to the government's figure of 37,000.

"The report itself is not having a go at the childcare policy itself," Professor Phillips said.

"It's actually quite positive in that we do show that there's considerable more winners than losers."

Professor Phillips, who works at the ANU's Centre for Social Research and Methods, added that his report shows the new package tends to support lower, rather than higher income families.

Early Childhood Australia continued to express concerns that vulnerable children would miss out on childcare because of the increased work requirement for parents.

"We urge all senators who vote on the childcare package to be fully informed of its impact," chief executive Samantha Page said.

The childcare package will provide all children from low income families with 12 hours of subsidised care a week. Early Childhood Australia is calling for all children, regardless of family income, who are three and under to have a basic entitlement of 18 hours of subsidised care a week.

"There are many complex reasons why families might fail the activity test. All it takes is for one parent to be in irregular work, experience an illness ... and the family will lose their entitlement," Ms Page said.

The ANU modelling relies on the Australian Bureau of Statistics survey of income and housing data, which is different from the government's own administration data.

Senator Birmingham, who has responsibility for childcare, said the government's analysis was "based on a 'complete picture' and actual outcomes that take all factors of the Jobs for Families package into calculation".

He added the government wanted to "better help parents who want or need to work ... while still supporting early childhood education."

Professor Phillips' report notes that while the government's data base was "superior" in terms of information about the number of families accessing childcare, the hours used and prices charged, it lacked detail on the hours parents worked.

The new data comes as the Senate conducts an inquiry into the childcare bill on Friday.

With more than 100 submissions to the inquiry and concerns from human rights, welfare and childcare organisations about the detail of the package, some groups have expressed frustration that only a half-day hearing - with four witnesses - has been scheduled.

Family Day Care Australia, who has not been called, said it was concerned about the "lack of thorough assessment".

The "Jobs for Families" package will replace two childcare payments with one and will see childcare subsidies vary, based on how much parents earn and how many hours they work.

The Coalition says the package is "contingent" on the Senate also passing savings to family tax benefits, to fund the planned extra $3 billion investment in the sector.

So far, it does not have the numbers to do so.

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