Here in the USA, there is one manufacturer that I know of that has "kiddie-resistant" sockets with spring loaded shutters behind the two plug holes. Apparently it works on the principle of equal pressure from the plug pins. I don't know, never bought one.
If you don't want to go that route, however, there are wallcovers with spring loaded turnable covers that spring shut when you pull the plug out. These go in place of the standard cover.
