Mr Abbott has responded by accusing Ms Gillard of carping and says the government is demonstrating "more spin and relentless negativity".
He says the government is "running scared" of a Productivity Commission inquiry into more effective childcare arrangements.
Mr Abbott launched a national debate on childcare this week when he declared that a coalition government would ask the Productivity Commission to examine how to make childcare more flexible through extending the 50 per cent childcare rebate to the cost of employing a nanny.
Ms Gillard on Saturday latched onto a comment from an unnamed Liberal MP who was quoted in Fairfax newspapers as saying no-one really believed the coalition would implement the scheme, and that it was just part of an appeal for women's votes.
She said the comments showed the plan was simply a ruse to convince women that the coalition really cared about them, adding that people should look to "the cynicism that dripped from this scheme".
"(It's a) very frank admission from the Liberal party today that this was all about politics and not about real benefits for working women," Ms Gillard told journalists in Brisbane.
"Really this was just a way of suckering women to make it look like they cared about childcare costs."
Childcare Minister Kate Ellis said costings by the Department of Education, Employment and Workplace Relations, based on average nanny's pay of $25-an-hour, showed Mr Abbott's scheme would cost $2 billion over four years.
"What that means ... is that 654,000 Australian families on childcare benefits would be looking at a 20 per cent cut to those benefits," she said.
Finance Minister Penny Wong said Mr Abbott had no economic credibility.
"His latest idea would cost $2 billion ... $2 billion over the forward estimates ... $2 billion which would add to his already enormous black hole," Senator Wong said.
Mr Abbott said this was just more spin and relentless negativity from a government acting more like an alternative opposition.
"If the Productivity Commission was good enough to look at disability insurance ... to look at aged care reform, why is the government running scared of a Productivity Commission inquiry into more flexible and more effective childcare arrangements within the existing funding envelope?" he told reporters in Cooma.
"Why shouldn't we be a little bit more flexible and a little bit more effective and a little bit more family friendly in our childcare arrangements?"
Greens Senator Sarah Hanson-Young said Mr Abbott's unfunded plan of just extending the childcare rebate to nannies was not the silver bullet for many parents' childcare dilemmas.
"But neither is the government's ignorant view that there's no problem that needs fixing," Senator Hanson-Young said in a statement.
"There are many parents who struggle with inflexible childcare arrangements and the government needs to find a way of funding more accessible and quality care options that are affordable for families who need the most support."
What do you think about the Coalition's proposal to extend the rebate to the cost of employing a nanny?
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