WASHINGTON, Jan 26 (Reuters) - Meta Platforms, TikTok and YouTube will face courtroom scrutiny this week over allegations that their platforms are fueling a youth mental health crisis, as the national debate about kids’ screen time enters a new phase.

The trial in California Superior Court, Los Angeles County is a test case for thousands of other lawsuits seeking damages for social media harms, in a legal onslaught that could erode Big Tech's longstanding legal defense.

The plaintiff is a 19-year-old woman from California, identified as K.G.M., who says she became addicted to the companies’ platforms at a young age because of their attention-grabbing design, according to court filings. She alleges the apps fueled her depression and suicidal thoughts and is seeking to hold the companies liable. Jury selection in the case begins on Tuesday.

Her lawsuit is the first of several cases expected to go to trial this year that center on what the plaintiffs call “social media addiction” among children. It will be the first time the tech giants must defend themselves at trial over alleged harm caused by their products, the plaintiff's attorney Matthew Bergman said.