A federal trial targeting Meta over the alleged harmful effects of its social media platforms on children opened Monday, with state attorneys general presenting opening arguments in what legal observers are calling a landmark case for tech accountability and youth mental health.

California Attorney General Rob Bonta led the charge for the states, arguing that Meta knowingly designed Instagram and Facebook with features that exploit adolescent psychology, foster addictive behavior, and expose young users to harmful content. The states are seeking restitution for children harmed by the platforms.

Meta's attorneys pushed back in their own opening statements, contending that the company has invested heavily in parental controls and safety tools, and that the platforms themselves are not the cause of broader youth mental health challenges. The company is expected to argue that external factors, including the COVID-19 pandemic and pre-existing social pressures, are more significant contributors to teen mental health struggles.

The trial consolidates complaints from dozens of states and is being watched closely by lawmakers, child advocacy groups, and the tech industry. It follows years of congressional scrutiny and internal whistleblower disclosures about the company's awareness of potential harms to younger users.

The outcome could have sweeping consequences for how social media platforms design their products and whether they face financial liability for user harm, potentially reshaping regulatory standards across the industry.