Utah is famous for its stunning natural landscapes and the Sundance Film Festival. But it also happens to be America's youngest state thanks, in part, to its Mormon population which tends to have larger families. One in three residents is under the age of 18, and the cohort is about to become the subject of a bold experiment to try to counter America's youth mental health crisis. Under 18s will soon be prevented from even signing up for social media apps without their parents' consent under sweeping new laws. The legislation will also give parents access to their teens' social...