The government needs to switch into “enforcement mode” and take on tech giants over its social media ban after doubling fines, experts have warned.

The federal government announced on Sunday it would introduce new legislation to double fines to $99m for platforms that breach the social media ban, and give the eSafety commissioner, Julie Inman Grant, stronger information-gathering powers.

Research this month suggested the majority of under-16s were bypassing age restrictions.

The government said more than 5m accounts have been removed, deactivated or restricted since the ban was introduced on 10 December.

But Catherine Page Jeffery, a senior lecturer in media and communications at the University of Sydney, said it was clear the government needed to do more to crack down on the platforms.

She said digital duty of care legislation would help protect all users from the harms of social media.

“It is still early days yet not much has changed for under-16s with about 80% still stating they remain on social media,” she said.

“Stronger enforcement mechanisms are clearly needed, but there’s no point in doubling the penalty if the regulator doesn’t enforce them, and move into the enforcement mode.”

Page Jeffery said the under-16s ban eroded the rights of young people online, and that the platforms should be held more accountable for the content they carried.

“This digital duty of care is really vital, and I think this would be much better policy rather than excluding younger people, because then it places this obligation on the platforms to be more proactive about making sure their platforms are safe, and that will include more transparency around algorithms,” she said.

The government has promised to legislate a digital duty of care, but is still consulting on what form it would take.

The Greens on Sunday called for the government to focus on that legislation, and use it to regulate social media algorithms.

“When this [social media ban] legislation was debated, the Greens argued that we needed to regulate the algorithms, not just the symptoms. The two major parties chose not to,” Greens senator Sarah Hanson-Young said.

“If the prime minister really is serious about staring down the big tech companies, he’s got to tackle the algorithms.”

Hanson-Young said her party would consider the new legislation increasing fines for non-compliance, but promised to push for action on algorithms.

The treasurer, Jim Chalmers, acknowledged the tech companies had not been doing enough.

“We will strengthen the penalties. We will strengthen the powers of the eSafety commissioner, and that’s because we recognise that the future of our kids, the safety of our kids, is too important to let the big tech companies wriggle off the hook or avoid their responsibilities,” Chalmers told the ABC’s Insiders program.

The shadow communications minister, Sarah Henderson, said the new penalties were an “admission of failure” by the government.

“Today’s announcement is an embarrassing admission that Anika Wells’ oversight of the social media ban has been flawed and chaotic which is compromising the online safety of children,” she said.

Earlier this month, the Murdoch Children’s Research Institute released a study which found a direct risk between heavy social media use and poor mental health in young people – with adolescents aged between 12 and 13 the most vulnerable.

But it also warned age-based restrictions alone were unlikely to eliminate all risks.

“This includes holding social media platforms accountable for algorithms and features that promote compulsive engagement and exposure to harmful content. One way to achieve this is through Australia’s proposed digital duty of care reform,” authors of the report urged in The Conversation.

Experts welcomed the penalties being aligned with other fines under competition law, but questioned whether it would have the desired compliance effect.

Elizabeth Handsley, a Western Sydney University law professor and president of Children and Media Australia, said giving Inman Grant more powers was “worth a try”.

“It’s nice to think this kind of matter is being treated as seriously as the other kinds of corporate breaches that our law addresses,” she told ABC radio.

“Whether its going to be effective, you have to presume the government has done its homework and that it has reason to believe it’s going to be so.”

TikTok, Snapchat, Meta, which owns Facebook and Instagram, and Google, which owns YouTube, were approached for comment.