China prohibits children under the age of 18 from playing video games for more than 3 hours a week. This is a harsh social intervention that he said was necessary to prevent an increase in addiction to what was once called “mental opium.” The new rules, announced on Monday, are part of Beijing’s major shift to strengthen control over society and key sectors of the economy, including technology, education and real estate, after years of runaway growth. The restrictions that apply to all devices, including phones, will hit the global gaming industry with tens of millions of young players in...