You have to make everyone abide by them, for it to not-suck. At a minimum, software and service providers would have to respect settings client agents tell them they have (as in the AppleTV case, it's bordering on pointless for platforms to even have them if most vendors ignore them)
That'd probably be enough (plus something for school devices in particular to let parents set stricter settings during non-school hours, without having full admin rights on the devices) to do a ton of good, but it's not a startup, it's a protocol and maybe a law.
The startup version would probably try to capture that as some kind of one-stop-shop web portal.
I would think that as a platform like this grows, they would be able to build relationships with OS and service vendors to manage parental control settings via API. After all, this would take a lot of public pressure off of the individual vendors, especially for social/gaming/media platforms.
That'd probably be enough (plus something for school devices in particular to let parents set stricter settings during non-school hours, without having full admin rights on the devices) to do a ton of good, but it's not a startup, it's a protocol and maybe a law.
The startup version would probably try to capture that as some kind of one-stop-shop web portal.