What good is it if it is voluntary. The money making sites have been .com for decades and they arent going to change voluntarily. There would have to be clear standards. Any nudity other than medical related perhaps?
You can lock down your browser so that it can only goes to particular sites and if you try to go to a site that isn’t whitelisted, then you have to enter a password. That’s a simple solution that doesn’t involve the creation of a cabinet level federal agency.