A US court fined Meta $942 million over children, then ruled it could not make the company check anyone's age. Australia already forces that, and eight in 10 under-16s are still on.

Judge Bryan Biedscheid called Meta a public nuisance akin to air pollution, adding a $567 million fund to the $375 million a jury imposed in March.

A New Mexico judge has called Meta a public nuisance and ordered it to pay $US567 million ($A806 million) into a fund to repair what its apps did to children.

Judge Bryan Biedscheid compared the company to air pollution.

"Significant numbers of people in New Mexico experience harm from Meta's products due to risks of sexual exploitation, interference with education, and adverse mental health outcomes," his order said.

The fund sits on top of $US375 million in civil penalties a jury imposed in March, taking the total to $US942 million. Of the fund, $US420 million goes to treatment services for young people.

The jury found Meta committed 75,000 violations of New Mexico's Unfair Practices Act and applied the maximum penalty to every one. It found the company knowingly harmed children's mental health and concealed what it knew about child sexual exploitation on its platforms.

Attorney-General Raul Torrez brought the case in 2023, after state agents built a fake profile of a 13-year-old girl and watched what happened.

Platforms removed 4.7 million under-16 accounts in the first five weeks of Australia's ban. Meta accounted for more than 544,000 of them. Photo: The Glass

The judge also ordered changes inside New Mexico. Like counts hidden from under-18s unless a parent approves. Push notifications to minors paused between 10pm and 7am. Usage capped at 90 hours a month, about three hours a day.

Then he set out what he could not do.

He could not order Meta to verify anyone's age. Federal privacy law bars the court from making the company collect personal data from children, even to establish how old they are.

He also found that requiring age verification of Meta alone, and not of every other platform, would be "inequitable and unduly injurious" to the company.

Australia answered both of those problems eight months ago.

The under-16 ban took effect on December 10 and applies to 10 platforms at once, not one. It puts the obligation on the companies rather than on children or parents. Systemic breaches carry fines of up to $49.5 million.

Platforms removed 4.7 million under-16 accounts in the first five weeks. Meta accounted for more than 544,000.

In March the government widened the rules to name the design features it holds responsible - infinite scroll, like counts, disappearing stories. The same list the New Mexico judge reached for.

Last week the eSafety Commissioner reported that more than eight in 10 Australian under-16s are still using social media.

Facebook, Instagram, Snapchat, TikTok and YouTube are all under investigation for potential non-compliance. None has been fined.

Anthony Albanese has since doubled the penalties and handed the regulator stronger powers to compel platforms.

One country cannot make Meta check. The other can, and did.

Neither has the children off the platforms.