On Android the most reliable method I've found is to create another Google account, set it up as your "parent", then (while logged into that account) go to fami

On Android the most reliable method I've found is to create another Google account, set it up as your "parent", then (while logged into that account) go to familylink.google.com and set app and content limits for the "child". You can block individual apps, set daily time limits for apps, and whitelist websites for browsers.