It was not Yang Qingning’s millions of social media followers or her political beliefs that made the young woman the scorn of Chinese state media recently. It was her tiny baby. Two of China’s most popular video platforms disappeared from app stores this week after the state broadcaster CCTV accused them of promoting underage pregnancy. A segment last week on CCTV featured what it said were teenage women whose videos — chronicling the joys and tribulations of motherhood, complete with images of swollen bellies — had attracted millions of followers and viewers. A stern but unspecific rebuke from China’s top media regulator followed a few days later.