The answer maybe lies in producing a combined firewall/router that the user can download a blocked sites list into...
That is still a long winded solution and not one that is perfect because all sites not on the list would still get through.
If all adult content had to use a .xxx domain then all the browser/firewall/software would need to do is stop any content from a .xxx domain loading. Simple solution and problem solved.
But if the government implemented it all it can do is look at some list they or some third party they engage for sites and/or look for keywords in URLs, page text etc... and all those solutions are obviously un-implementable (not sure if that's a real word
How can anyone limit porn sites to using the xxx top level domain? What's to stop me from just going and setting up a porn site on a .co.uk or .com? Those tlds already get misused left, right and centre, .com is supposed to be for American corporate websites (although it is so misused over the years that every one has totally disregarded that). The only way it could work would be to block sites on on "xxx" if they are found to contain "dodgy" stuff afterwards and I believe the saying "shutting the stable door after the horse has bolted" applies here! Not to mention, who decides what is "dodgy".
The idea of stopping children accessing shocking material is a totally sound one and I don't think any one could disagree with that but there is no way of doing it, the very nature of the Internet prohibits it from being possible. All we will end up with is larger bills from ISPs who are forced to spend a fortune on some system that is a failure before it's started and perhaps worse, governments attempting to control what we can and can't access.