The country's internet regulator eSafety has voiced "significant concerns" about the extent to which Facebook, Instagram, TikTok, YouTube and Snapchat are working to keep children off their platforms.
Late last year, a law came into effect banning users under the age of 16 from using 10 social media platforms.
As reported by the BBC, eSafety has completed its first report since the ban was put in place in December, and the organisation has spotted "a number of poor practices" from the five platforms.
These include enabling those under 16 to repeatedly "attempt the same age assurance method", as well as giving children who had already declared they were under 16 before the ban the opportunity to show they were over the threshold.
It's also said there have been insufficient measures preventing new under-16 users from creating accounts, along with no effective ways for people to report under-16s who have access to social media.
eSafety Commissioner Julie Inman Grant said: "While social media platforms have taken some initial action, I am concerned through our compliance monitoring that some may not be doing enough to comply with Australian law."
In January, the regular reported that 4.7 million accounts had either been restricted or removed in the first month of the law being in effect.
However, Grant explained the regular will now start enforcing restrictions and gathering evidence.
She explained: "The evidence must establish the platform has not taken reasonable steps to prevent children aged under 16 from having an account.
"That means more than simply demonstrating some children do still have accounts. Rather, the evidence must show the platform has not implemented appropriate systems and processes."
Meta - which owns Facebook, Instead, WhatsApp, Threads and Messenger - insists the company remains "committed to complying with Australia's social media ban".
A spokesperson speaking to the BBC argued that "robust age verification and parental approval" at the app store level if the best way to protect young people, while it said accurate age determination remains "a challenge for the whole industry".
Meanwhile, Snapchat developer Snap noted 450,000 accounts have been locked thus far, with more coming "every day".