AC power socket protection cap

Did not found this simple thing in this big data base.Created.
The progress of technologies complicates to children access to AC power sockets, only the most gifted perish
At Former Soviet Union kids always put their fingers into AC power socket and get problems of curiosity. We had such thing that protects our kids from problems :) It is possible to put into the socket but very difficult to remove it. Only adult parents can do that.

P.S. it can be removed from socket only by screwdriver