All parental moderation mechanisms can and should be implemented as opt-in on-device settings. What governments need to do is pressure companies to implement those on-device settings. And what we can do as open-source developers is beat them to the punch. Each parent will decide whether or not to use them. Some people will, some won't. It's not Bob's responsibility to parent Charlie's children. Bob and Charlie must parent their own children.
To the people arguing that parents are too dumb to control their children's tech usage because they themselves are tech-illiterate: millennia ago, we invented this new thing called fire. Most people were also "too dumb" to keep their children away from the shiny flames. People didn't know what it was or how dangerous it could be. So the tribe leader (who, by the way, gropes your children) proposed a solution: centralize control of all the fire. Only the tribe leader gets to use it to cook. Everyone else just needs to listen to him. Remember, it's all for you and your children's safety.