Sarah Meier, an industrial relations lawyer at a top tier firm, and president of the Australian Labour and Employment Relations Association ACT, said parents might also find themselves vicariously liable for an injury caused by a negligent act of an au pair.

Traditional agencies that provide nanny services usually provide them with workers' compensation insurance.

However, the growth of online jobs platforms has meant that some families were now bypassing those agencies and directly sourcing labour on the internet from nannies and au pairs, particularly from overseas.

Ms Meier told the Industrial Relations Society of NSW annual conference at the weekend that some budget-conscious families are avoiding childcare fees of around $100 per day by hiring a live-in child carer for about $250 per week through online jobs platforms.

"It is becoming a more and more common way of structuring childcare and domestic work arrangements in Australia," she said.

"Online connection platforms are connecting families with au pairs from overseas on a scale not seen before."

Ms Meier , who has just completed a thesis on domestic arrangements in Australia for a masters of laws, said there was one case that had been before the courts in New Zealand. It was found the au pair was an employee of the family, which meant they were required to provide associated payments and entitlements.

"There is some uncertainty around whether or not an au pair would be held to be in an employment relationship with their host family in Australia," Ms Meier said.

Au pairing originally provided an opportunity for cultural exchange. However, it is now used by some to access domestic help from 9am to 5pm, with little regulation.

The status of the au pair working arrangement is not clear and has not been tested before an Australian court.

"A lot of families do not think too deeply about the legal implications of these relationships and do not pay minimum wages. If the question were to come before a court in the context of an underpayments claim it could mean a family is not only liable for back-paying an au pair, they could also be liable for penalties if it is found to be an employment relationship," Ms Meier said.

"Families may also be obligated to make compulsory superannuation payments if their au pair or nanny works for them for more than 30 hours per week.

"If they don't have workers' compensation insurance, parents may ultimately end up footing the bill for everything from a slip and trip in the household to a car accident which leaves the au pair incapacitated."

There is also a risk that if an au pair injured a child in their care, for example by dropping them, the family may be vicariously liable for the au pair's negligence and subject to a common law claim for compensation.

"There are vulnerabilities for the workers and for the families who may not know what they are potentially opening themselves up to," she said.

Given the prevalence of the use of au pairs, Ms Meier suggests it may be just a matter of time before the law in this area is tested.

"It is not something that has been really tested in the Australian jurisdiction," she said.

Arrangements can vary from au pairs working three to 10 hours per day in exchange for board, meals and a payment.

Marian Baird, Professor of Gender and Employment Relations at the University of Sydney Business School and president of the NSW Industrial Relations Society, said childcare remains a major concern for Australian families.

"The changes introduced in the new childcare package which cut subsidies to high-income households, run the risk of those families seeking other forms of childcare, including the possibility of seeking au pairs from overseas whose working conditions are not appropriately regulated," she said.