By putting these, or any other socket covers in your UK power sockets, you have over-ridden the safety features which make UK sockets already safe by design, and made your children less safe.
UK sockets have a shutter which covers the live and neutral contacts until a plug is inserted. Socket covers provide your child with a tool to get around these safety features in a number of ways.
Don't waste your money on these items - you don't need them at best. At worst you have provided your kids with a dangerous toy.
A search for Fatally Flawed on the internet will take you to a site illustrating the problems with socket covers.