The move comes as evidence suggests children are still able to access the platforms six months after the world-first restrictions took effect in December.
Australia's implementation and enforcement of the ban is being closely watched by dozens of countries who have either created or committed to creating their own such laws.
STILL TOO MANY CHILDREN ON SOCIAL MEDIA, PM SAYS
Prime Minister Anthony Albanese said there were still too many children on social media and tech firms were not doing enough to comply with the ban.
"We're calling time on the social media companies today and doubling down on the changes that we have made and that we're prepared to make," he told reporters in Canberra.
"Today, we'll introduce legislation this afternoon that goes further to ensure social media companies are doing everything within their power to stop children under 16 being on their platforms."
The internet regulator, eSafety, is investigating possible non-compliance by five platforms: Meta's Facebook and Instagram, Snapchat, TikTok and Google's YouTube.
There was no immediate comment from Meta, Google and Snapchat. TikTok declined to comment.
Albanese called on the Coalition opposition to back the bill, noting the original policy passed with bipartisan support.
The changes, announced on Saturday, would double maximum penalties to A$99 million ($68.2 million) from A$49.5 million.
They also give the eSafety Commissioner power to compel documents such as company board minutes and internal emails, ensuring legal cases being built against platforms failing to comply are as "strong as possible", said Communications Minister Anika Wells.
"DIRTY TRICKS" USED TO UNDERMINE BAN, MINISTER SAYS
Introducing the bill to parliament, Wells accused the firms of deliberately failing to comply and using "dirty tricks" to undermine the ban.
"Today Australia is sending a message to those companies: we see what you're doing, we are not here to play games. If you want to do business in Australia, you will comply with Australian laws. And if you don't, you will face the consequences," she said.
Sydney resident Bill Wright said he was glad the government was taking more action to hold social media companies accountable.
"We may be leading the world in some of the problem-solving but obviously we've got a lot more to do," he said.
"The money that we are going to be trying to fine companies for not doing the right thing still may be not enough."
The new legislation requires parliamentary approval before it takes effect.
Posted by: Alma Angeles/NET25 News
