The decision came after the internet regulator urged the government last month to overturn the YouTube carve-out, citing a survey that found 37 percent of minors reported harmful content on the site, the worst showing for a social media platform.

"I'm calling time on it," Prime Minister Anthony Albanese said in a statement highlighting that Australian children were being negatively affected by online platforms, and reminding social media of their social responsibility.

"I want Australian parents to know that we have their backs."

The decision broadens the ban set to take effect in December. YouTube says it is used by nearly three-quarters of Australians aged 13 to 15, and should not be classified as social media because its main activity is hosting videos.

"Our position remains clear: YouTube is a video sharing platform with a library of free, high-quality content, increasingly viewed on TV screens. It's not social media," a YouTube spokesperson said by email.

Since the government said last year it would exempt YouTube due to its popularity with teachers, platforms covered by the ban, such as Meta's Facebook and Instagram, Snapchat and TikTok, have complained.

They say YouTube has key similarities to their products, including letting users interact and recommending content through an algorithm based on activity.

The ban outlaws YouTube accounts for those younger than 16, allowing parents and teachers to show videos on it to minors.

"Teachers are always curators of any resource for appropriateness [and] will be judicious," said Angela Falkenberg, president of the Australian Primary Principals Association, which supports the ban.

Artificial intelligence has supercharged the spread of misinformation on social media platforms such as YouTube, said Adam Marre, chief information security officer at cyber security firm Arctic Wolf.

"The Australian government's move to regulate YouTube is an important step in pushing back against the unchecked power of big tech and protecting kids," he added in an email.

The reversal sets up a fresh dispute with Alphabet, which threatened to withdraw some Google services from Australia in 2021 to avoid a law forcing it to pay news outlets for content appearing in searches.

Last week, YouTube told Reuters it had written to the government urging it "to uphold the integrity of the legislative process". Australian media said YouTube threatened a court challenge, but YouTube did not confirm that.

"I will not be intimidated by legal threats when this is a genuine fight for the well-being of Australian kids," Communications Minister Anika Wells told parliament on Wednesday.

The law passed in November only requires "reasonable steps" by social media platforms to keep out Australians younger than 16, or face a fine of up to A$49.5 million.

The government, which is due to receive a report this month on tests of age-checking products, has said those results will influence enforcement of the ban.