Add Yahoo as a preferred source to see more of our stories on Google. Back-to-school season often means new clothes, sharpened pencils, and freshly packed backpacks. But today, there’s another item parents need to keep an eye on: the digital backpack.

Some of the world’s biggest tech companies are facing landmark trials that could alter the outlook of the social media industry when a jury decides whether their platforms are addictive and hurting young people. The first in a series of trials started in ...