Parents and experts have claimed for years that social media is addictive and damaging to children's mental health. Now, a lawsuit against Meta and YouTube in L.A. wants to prove big tech knew about these risks.Advocates are calling this Big Tech's "Big Tobacco's moment" because the outcome of the trial will set a precedent for thousands of other cases, could result in billions of dollars in payouts, and changes to how social media platforms are allowed to operate.