Everyone knows that electricity is dangerous… that is, everyone except for young children. All they know is that they see their parents use the wall receptacles to plug in all kinds of things to get them to operate. Can you really blame them for wanting to stick things into the wall receptacles as well? While telling them about the danger that electricity poses, it might be necessary to take some extra steps to prevent them from getting hurt, especially if they are very young.
Some parents have chosen to insert plastic plugs that will block access, but the problem with these is that children can be very persistent when they have gotten an idea in their minds, and those plugs can be easily forgotten after you use the receptacle.
A better solution is to install a tamper-resistant receptacle. These are made in such a way that it is impossible to insert something in just one side of the receptacle. You need to have a two-pronged contact inserter with even pressure on both sides for the receptacle to open up. This could save the life of your child, so it is a worthwhile investment.