I like the first part of the idea, which is the header. Heck, even enable it by default. As long as the tracking of the toggle isn't a thing its a perfect compromise. While we're at it, respecting do not track headers would also be nice.

This completely leaves it up to the families / parents to control and gives some level of compliance to make the effort worth while.

There may even be a way to generate enough noise with the request to prevent any forms of tracking. This sort of thing should really be isolated in that way to prevent potential abuses via data brokers by way of sale of the information