CA tried this with AB 1856. I wasn't a fan of this (neither was EFF) because of the privacy and tracking concerns of blasting the fact that the user is a child to all websites.
https://www.eff.org/deeplinks/2026/05/one-step-forward-two-s...
It would better for the block to happen at the device level. That is, the browser knows it's on a child's device and has a whitelist of allowed sites.
There is already an RTA (Restriced to Adults) header where the website self-labels that it's for adults only and the browser can block it while protecting the user's privacy. I'd prefer expanding the use of RTA.
The web is too big and changes too much and that's before we get to the issue of applying laws to a whitelist based on different juristictions worldwide.
And I have to question, who would administer it? The parents? They won't. Google or Apple? Why do they want to deal with irate parents or culture wars around what is or is not on the list?
There is obvious increasing demand for this from parents, politicians are going to act on it, I think a "this is a child" header is the only one that actually really works. It works for the parents because it's easy to setup. It works for websites because they can cleanly identify a child and filter content if appropriate.
It seems to me that every other solution than a "this is a child" header is either impractical or way worse.