Electric cars have been around since the 1800’s. Modern electric cars drive circles around their predecessors.
Believe it or not, an electric cars works on the same principles that power a remote-controlled car you can buy in a department store.
Basically, you charge a battery from a power source that powers a motor that turns the wheels.
Of course, a full-sized car has other systems that need to be powered but the basic principle is still the same.
Explain That Stuff! has a comprehensive article on electric cars and how they work.
How Do All-Electric Cars Work? is a nice one-page explanation that you can show younger kids.