Ads are highly regulated in the EU and individually in member countries. Eg. in Poland it's illegal to show ads using TV shows for children, the ads before and after a show have to be child safe, eg. no medications. Yet same rules don't apply to YouTube or Facebook. Why wouldn't I indicate using a header that this device is used by a child and ads must be appropriate?
I remember that this was trying to be a thing in the mid-2000s (via COPPA) in order to help better age restrict adult content. Sites would use metadata to signal the apropriate age limit for their content and web filters could use this to deny access. I don't think that ever went anywhere.
