This news out of China today. It intends to offer free or low cost Net connections for children, but "filtrate away harmful information."
Good luck. Just ask American schools how well that seems to work. Heck, I was even at a school a couple weeks back that intentionally proxied their own servers - because even they couldn't live with the filters.
No one knows filtering better than China (as I found out when there a couple months ago), but it doesn't seem to matter how thick you build the concrete ... the curious always seem to get through.