The UK has announced it is going to block social media for under-16s.
Prime Minister Sir Keir Starmer said that the ban would take effect in early 2027.
He said keeping children off social media was "the right step for Britain" and the best way to keep them safe online.
The ban will cover platforms including Snapchat, TikTok, YouTube, Instagram, Facebook and X, the government said.
An exhaustive list of which platforms the ban will apply to has not been released. However the government said it would apply to those "whose purpose is to enable social interaction and which allow users to post material".
The measures will also require platforms to prevent children from being able to livestream, including on gaming platforms.
The government said there would be a block on functions which allow strangers to communicate with children under-16. Restrictions on these functions would also be on by default for under 17s "to prevent a cliff-edge at 16".
It said it was also looking into overnight curfews and breaks in infinite scrolling for under-18s, with more detail on this to be set out in July.
AI "romantic companion" chatbots, which are designed to simulate sexual relationships or roleplay with users, will have to enforce a minimum age of 18.
AI chatbots more widely will have to restrict "intimate functionalities" for under-18s, the government said.
The government said it did not intend to include messaging services like WhatsApp and Signal in the social media ban.
Most social media platforms already require children to be over 13 to create an account and use their services.
The prime minister said the government plans to pass regulations before Christmas, which would allow the measures to come into place in early 2027.
He said the government had already introduced legislation allowing it to take this kind of action.
Among those who have been calling for social media to be banned for under-16s are bereaved parents and families.
Lisa Kenevan said her son Isaac, who died aged 13, has been her "driving force" in her campaign. She told BBC Breakfast that while parents wanted the ban "a lot sooner", the announcement means "we're in a good place now".
Mariano Janin, whose daughter Mia died at the age of 14 in 2021 after she was a victim of cyber bullying, said the announcement had left him "speechless".
"I think it's a change in the right direction, it won't be easy, but it will be possible," he said.
However, speaking ahead of the announcement, Ian Russell - whose daughter Molly took her own life at the age of 14 after viewing harmful content online - accused the government of rushing restrictions for political reasons.
Russell said "sledgehammer techniques like bans" only cause more problems.
Overall, nine out of 10 parents back decisive action on social platforms for children, according to the government.
However, some teens have expressed concern about how a social media ban will affect their ability to connect with friends and express themselves.
George, who is 14, told BBC Radio 4's Today programme he felt people his age should be able to make their own choices because "we're beyond people saying what we have to do".
Lilly, 15, from Cumbria said apps like TikTok allow her to "communicate more", for example by allowing her to post videos of her performing.
Of the platforms affected, only YouTube has commented so far.
It said it was concerned a blanket ban would push children away from "curated, supervised, beneficial experiences and towards anonymous, less safe services".
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