The only thing I can think of is a mass education campaign about parental controls on phones and tablets, and schools only allowing kids to use devices with parental controls enabled, while making the parental controls on phones and routers easier to use.

But kids will always find a way around that. And parents are lazy or don’t understand these things (parenting is very difficult, so I can’t blame them much).

I don’t think a Chinese style great firewall can work in countries like the UK.