The means-tested childcare benefit (CCB), which offers 24 hours a week of subsidised care regardless of whether a parent is working or studying, is being examined as part of the Productivity Commission's inquiry into creating a sustainable childcare system.

A potential scaling back of the CCB has been criticised by children's advocate Early Childhood Australia.

Australian Childcare Alliance president Gwynn Bridge said restricting the CCB for parents who are not working would deny disadvantaged youngsters an opportunity for early childhood education.

"There has been so much research into the value of early education and care, you would hate to see those vulnerable and disadvantaged children miss out," she said.

"Any fees are high fees for a lot of these families. We certainly are not seeing enough of the vulnerable and disadvantaged children attending early childhood education and care services as it is, so we would hate to see their access restricted."

She said providers already give priority to families where both parents are either working or studying.

Early Childhood Australia chief executive Samantha Page said children had a right to early childhood education regardless of their parents' circumstances.

Families earning under $42,997 receive the full rate of CCB, which is $4.10 an hour. The subsidy decreases as household income rises, cutting out completely at $149,597 for families with one child.

Ms Page said many families who are eligible for the full rate of CCB are in transient employment and restricting the subsidy would force them to remove their children from care.

"The reality for many families who claim CCB is that they are in and out of work all the time," she said. "It's not OK for kids to be in and out of services all the time."

She said children from vulnerable homes were more likely to thrive if they were given early educational opportunities.

"Disadvantaged children stand to benefit the most from attending good-quality day care centres with preschool programs," she said.

David O'Byrne, acting national secretary of United Voice, which represents the early childhood sector, said that while childcare allows parents to return to work, it also has many other advantages.

"Parents want their children to attend childcare for many reasons: enabling mothers to return to work is important, but it is by no means the only reason," he said.

"Parents and early childhood experts know that the benefits to children of quality early childhood education and care are immediate and lifelong. If a child would benefit from childcare, that child should be able to attend, regardless of whether his or her parents have jobs."

The office of Assistant Education Minister Sussan Ley, who has responsibility for childcare, was unable to provide figures on how many non-working parents are claiming the CCB, however Ms Ley said the subsidy existed "principally to allow parents to participate in the workforce".

Maroubra mother Tracey Willmot still takes her three-year-old son to childcare despite being on maternity leave with her 10-month-old daughter.

"He is learning so much there and he's really enjoying it," she said. "I just don't think he would get the same level of stimulation at home."

The Productivity Commission is due to hand down its draft report this month.