LOS ANGELES (AP) — 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's parent company Meta and Google's YouTube face claims that their platforms deliberately addict and harm children. TikTok and Snap, which were originally named in the lawsuit, settled for undisclosed sums.

Jurors got their first glimpse into what will be a lengthy trial characterized by dueling narratives from the plaintiffs and the two remaining social media companies named as defendants. Opening arguments in the landmark case began Monday at the Spring Street Courthouse in downtown Los Angeles.

Mark Lanier delivered the opening statement for the plaintiffs first, in a lively display where he said the case is as "easy as ABC," which he said stands for "addicting the brains of children." He called Meta and Google "two of the richest corporations in history" who have "engineered addiction in children's brains."

At the core of the Los Angeles case is a 19-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 and what damages, if any, may be awarded, said Clay Calvert, a nonresident senior fellow of technology policy studies at the American Enterprise Institute.