This is funny but actually has sort of existed for decades, in the sense of the TV watershed – no adult content before 9pm, after which point it's assumed children are in bed and not watching TV.
And yes, you are absolutely right that parents do often like these laws. Being a parent is hard, whatever the age of the kids, and parents will be in favour of things that make it easier. Whether that's making TV default-safe in the daytime, or making adult websites harder to access.