Okay so one thing nobody mentions is that even after you block TikTok using Family Link or router settings, kids can still access it through a browser. Like they just go to tiktok.com on Chrome and boom, they are scrolling 
So make sure you also restrict browser access or at least turn on SafeSearch and block specific websites. In Family Link, go to Google Chrome settings under your child’s profile and you can set it to “only allow approved sites.” That way the browser is also locked down.
Also worth noting that if your child uses a school-provided Google account, Family Link may have limited access to that device so double check which account is active on their phone. This burned a friend of mine who thought she had everything blocked but the school account bypassed all her settings. Real scenario from real life, not making that up 