(Corrects final paragraph to say Spain has proposed a social media ban for underage users, not enacted)

By Jody Godoy

LOS ANGELES, Feb 9 (Reuters) - Meta Platforms and YouTube deliberately designed products they knew would addict children, a lawyer for a woman suing the two companies told jurors in California on Monday at a trial that will test whether Big Tech platforms can be held liable for their app design.

The 20-year-old woman identified as Kaley G.M. in court is suing ​Facebook and Instagram parent company Meta Platforms and Alphabet's Google, which owns YouTube.

Kaley was hooked on ‌social media at a young age because of the apps' addictive design, her lawyer Mark Lanier told jurors. Lanier said that internal company documents show that, "these companies built machines designed to addict the brains of children, and ⁠they did it on purpose."

Meta's attorney Paul Schmidt said in his opening statement that Kaley's health records show a history of verbal and physical abuse and ⁠a fraught relationship with her parents, who divorced when she was three years old. 

"If you took Instagram away and ‌everything else was the same in Kaley's ‌life, would her life be completely different?" he asked.

YouTube's lawyer is expected to give an opening statement on Tuesday. Both companies have denied the allegations.

A verdict against the tech companies could smooth the way for similar ​cases in state court, and shake the industry's longstanding U.S. legal defense against claims ‌of user harm. Google, Meta, TikTok and Snap face thousands of lawsuits in California. 

Meta Platforms CEO Mark Zuckerberg is expected to be called as a witness at the trial, which is likely to stretch into March. TikTok and Snap settled with Kaley before the trial.

Kaley ​is also expected to testify. She alleges the apps fueled her depression and ​suicidal thoughts and she ‌is seeking to hold the companies liable for worsening her mental health.  

Her lawyers aim to show that the companies were negligent in their design of the apps, that they failed to warn the public about the risks, and that the platforms were a substantial factor in her ⁠injuries. If they succeed, the jury will consider whether to award her damages for pain and suffering, and could also impose punitive damages.

Meta and Google ⁠plan to defend themselves from the claims by pointing to other factors in Kaley's life, laying out their work on youth safety, and trying to distance themselves from users who upload harmful content.

Los Angeles Superior Court Judge Carolyn Kuhl, who is overseeing the trial, instructed jurors that the companies cannot be held liable for recommending any content created by others, only for their own design and operation of the platforms.

Under U.S. law, internet companies are largely shielded from liability for material their users post. If ⁠the jury in this ‌case rejects that defense, it could pave the way for other lawsuits claiming the platforms are harmful by design.

SOCIAL ‌MEDIA FACES LEGAL BACKLASH

In addition to cases like Kaley's in state court, the companies face more than 2,300 similar lawsuits filed by parents, school districts and state attorneys ⁠general in federal court. The judge overseeing those is weighing the companies' liability protections ahead of the first trial over the claims in federal court, which could happen as early as June.

Also Monday, a jury in Santa Fe, New Mexico was hearing opening statements in the state's case accusing Meta of profiting from its platforms while exposing children and teens to sexual exploitation and damaging their mental health.

"It's true that in the United States that all companies have goals to make money," Donald Migliori, an attorney for the New Mexico attorney general, told the jury. But, he added, "Meta made its profits while publicly misrepresenting that its platforms were safe for youth, downplaying or outright lying about what it knows about the dangers of ​its platforms."

Meta's attorney Kevin Huff told the New Mexico jury the company has made extensive efforts to protect its users and has warned about the risk of bad content on its platforms.

The wave of litigation in the U.S. is part of a global backlash against social media platforms over children's mental health. Australia has prohibited access to ​social media platforms for users under age 16, and other countries including ‌Spain are considering similar curbs.