Jurors in a landmark social media case that seeks to hold companies responsible for harms to children got their first glimpse into what will be a lengthy trial characterized by dueling narratives from the plaintiffs and the two remaining defendants, Meta and YouTube. At the core of the Los Angeles case is a 20-year-old identified only by the initials "KGM," whose case could determine how thousands of other, similar lawsuits against social media companies will play out. She and two other plaintiffs have been selected for bellwether trials — essentially test cases for both sides to see how their arguments play out before a jury.

The world's biggest social media companies face several landmark trials this year that seek to hold them responsible for harms to children who use their platforms. Opening statements for the first, in Los Angeles County Superior Court, began on Monday. Instagram parent company Meta and Google's YouTube will face claims that their platforms deliberately addict and harm children. TikTok and Snap, which were originally named in the lawsuit, settled for undisclosed sums. This case marks the first time the companies will argue their case before a jury, and the outcome could have profound effects on their businesses and how they will handle children using their platforms.