A court has heard claims Meta intentionally hooked a generation of children on Facebook and Instagram, as the biggest legal challenge faced by the social media platform began.

A jury in Oakland, California will spend the next six weeks wading through claims by top attorneys from several US states and lawyers for the social media company.

A lawyer for California claimed Meta found "millions" of 11 and 12-year-olds were on Instagram and "did little to keep them off" as the trial opened on Tuesday.

Meta's representative said just over 100,000 such users were found, and argued that social media addiction does not exist.

California's lawyer said Meta knew its platforms hurt teen mental health, while Meta said it was being ignored how many more teens had good experiences.

The trial stems from a lawsuit filed in 2023 by 29 US states, including California and New York. They claim there have been numerous violations of federal and state privacy laws for children.

The states are seeking billions of dollars from Meta and are demanding it make changes to Instagram and Facebook, including ending "like" counts and infinite scroll.

In her opening arguments Megan O'Neill, a lead attorney for California, relied heavily on information found in millions of documents provided in the case from Meta. They included internal research, employee emails, and chat logs that went all the way up to Zuckerberg.

One piece of internal research on Instagram stated: "Teens have an addict's narrative about use."

In another that O'Neill pointed the jury to, Meta found "product features designed to increase time spent are inherently at odds with well-being and take away from people's ability to focus on activity that adds value to their lives".

Despite Meta's awareness of potentially negative impacts, O'Neill argued that Meta targeted young people as users of Facebook and Instagram. Meta, she said, went out of its way to "assure the public that its platforms were safe for kids".

O'Neill outlined to the jury how Meta's business model could be summed up. "Hook the users; hold them for as long as they can; harvest their data; hide the truth from the public when making public statements," she said.

She said that throughout the trial it would become clear that what Meta said publicly about its platforms and what its internal research showed were very different.

"Meta said it put safety over profits, but hid the reality that, time and again, when it came to make a decision, profits won."

Paul Schmidt, a lead attorney for Meta, directly addressed the internal research report O'Neill used in her opening arguments.

The Meta document O'Neill showed the jury found that "1 in 5 teens says Instagram makes them feel worse".

Schmidt said: "That sounds pretty bad."

"What else does the document say?" Schmidt went on. "That 41% of teens said it made them feel better and another 41% said it had no effect."

Schmidt also worked to poke holes in the states' argument that Meta had not only failed to stop users under the age of 13 from using its platforms, but that it intentionally "hooked" teens and children as users of Facebook and Instagram, or that they were designed to be addictive.

As for Meta being able to verify the age of every user on its platform, Schmidt argued that the very privacy laws Meta was being accused of violating had prevented it from saving and using data it needed to track underage users effectively.

Schmidt also argued a point that Meta has put forward in at other litigation this year - that social media addiction does not exist.

"There can be no dispute that Meta has recognised people struggle, or can struggle, with their use of social media, and has come up with tools to try and address that," Schmidt said.

He pointed to past statements from chief executive Mark Zuckerberg and head of Instagram Adam Mosseri in which they said Facebook and Instagram were not designed to be addictive. There is also no research that shows an addiction to social media is possible, he added.