Jurors in a landmark social media case that seeks to hold tech 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,

The world's largest social media companies have been accused of creating "addiction machines" as a landmark trial began in California examining the mental health effects of Instagram and YouTube.

Mark Lanier, the lawyer representing 20-year-old plaintiff identified by her initials "KGM" told jurors the companies "engineered addiction in children's brains," citing internal documents and researc...