National Minimum Wage 2012 Australia

It is important to note that Australia does not have an official au pair program.

For overseas Au Pairs, a visa that entitles the person to work must be obtained from the Department of Immigration.

Most people that may become an au pair would either use the Working Holiday Visa options or the Student visa to supplement their travel funds through incidental employment.

However there are limits on the number of hours that you can work under those visas.

Working Holiday Visa (Subclass 417)
Work and Holiday Visa (Subclass 462)

Student Visa’s: http://www.immi.gov.au/students/students/chooser/

An employer paying someone without a valid visa can be prosecuted, and the worker can be deported.
“as from 19 August 2007 it is an offence to knowingly or recklessly allow a person to work illegally, or refer an illegal worker for work.
Checking that all new employees have permission to work in Australia is the easiest way to avoid committing an offence.
Checks can be made using the Visa Entitlement Verification Online (VEVO) service”
People convicted of these offences face fines of up to $13,200 and two years’ imprisonment, while companies face fines of up to $66,000 per illegal worker.
The offences apply to employers, labour hire companies, employment agencies and anyone who allows illegal workers to work or refers illegal workers for work.

I am not sure how the wages work, although it seems that anyone working should be under the minimum wage umbrella.

It is an interesting point that needs looking at.