China limits social media because they repress free speech and political association. TikTok and other social media was a huge part of why there was such an outcry over the invasion of Ukraine and the genocide in Gaza. They doubly limit what kids can see because students are often hugely influential in political activism - especially in China, where students were an integral part of both the revolution(s) and Tiananmen Square. China’s gov is pants-shittingly terrified of another student-led revolution/crisis/etc and keep a very close watch on what the kids are saying and seeing.