How do we stop young children from looking at Internet sites that have inappropriate content?

It’s almost impossible for parents to stop their children from looking at inappropriate contents on the Internet since the current advanced technology makes them easily access the sexually explicit materials through internet or smart phones whenever and wherever they want to. It is so controversial over the ways of restricting children from accessing such contents. Many countries, civic groups and households have adopted many methods to protect children from inundated harmful obscene materials. Some governments enforce the regulation that blocks the internet access for children during certain hours. In Korea, some law makers have proposed a bill in which on-line game companies cannot operate after midnight to the next morning, aiming to protect children from game addiction. Some parents have the computer in the living room rather than in their children’s rooms, so children cannot watch porn or games. Smart phones are also another means of accessing the contents.