The prime minister has said he will "call time on a system that's failing our kids" as he prepares to announce changes to social media restrictions for children.
"This is a choice about whose side we're on: families across the country, or a status quo that isn't working," Sir Keir Starmer said.
While a government consultation has found a majority supports a social media ban for under-16s, some campaigners have said such sweeping measures would cause more problems.
The government's decision has not yet been made public. Media reports have suggested under-16s will be banned from a number of social media platforms and see restrictions imposed on other sites.
The Sunday Times reported the prime minister was set to announce a ban covering the same 10 platforms now prohibited for under-16s in Australia: TikTok, Instagram, Snapchat, YouTube, Reddit, Twitch, X, Threads, Facebook and Kick.
It said the UK would "go further" than Australia with additional measures including curfews for older teenagers and restrictions on AI chatbots.
According to the Guardian, under-16s will be barred from receiving or using disappearing messages and livestreaming on "safer" sites, and forced off "high-risk" ones altogether. Ministers have not confirmed the reports.
Sir Keir said: "How we keep kids safe online is one of the biggest debates of our time. As a dad, I know every parent wants their child to grow up safe and happy.
"This is a choice about whose side we're on: families across the country, or a status quo that isn't working.
"People rightly expect action, and this government will always stand up for parents and put children first.
"That's why we will call time on a system that's failing our kids and take bold action to give every child the best possible start in life."
Monday's announcement comes a fortnight after the government's three-month consultation closed.
As well as asking people's views on an outright ban, it put forward less dramatic interventions. These included switching off addictive features like infinite scroll and autoplay, curfews, strengthened age verification, and restricted AI chatbot use.
Some 90% of the 116,000 people who responded backed a social media ban for under-16s, with more than 83% saying the benefits of social media were outweighed by the risks.
The father of Molly Russell, who took her own life aged 14 after seeing harmful content online, told the BBC he would be "dismayed" should such bans come into force, having previously called instead for better regulation.
Ian Russell warned in January that an Australia-style ban would "create a false sense of safety", push children to other areas of the internet, and deprive them of connection. Organisations including the NSPCC, the Internet Watch Foundation and Childnet supported the message.
Russell told the BBC on Saturday that Sir Keir appeared to have "rushed" his policy for "a political reason".
"If he's playing politics, what he's doing is gambling with young people's lives - and I find that deplorable."
The culture secretary meanwhile told the BBC's Sunday with Laura Kuenssberg that technology firms had had "more than enough time to get their house in order".
Lisa Nandy said she would not pre-empt Starmer's announcement but said it was "how, not whether, we better protect children online". She also pointed to the support for a ban during the consultation.
She acknowledged the ban in Australia had shown some young people would find ways to avoid restrictions.
But she said it still created a worthwhile cultural change: "At the ages of 8, 9, 10 and 11, children aren't presuming they are going to be in these spaces because all of their friends are."
