Okay kiddo, so a long, long time ago, people believed that there were five different suns in the sky. Each sun took turns shining down on Earth for periods of time before going away and letting another sun take its place. But one day, these five suns all appeared in the sky at the same time, causing the Earth to become extremely hot and causing a lot of problems for people and animals. So a brave hero named Nanahuatzin decided to sacrifice himself by jumping into a big fire to become a new sun and save the Earth. And that's how we ended up with just one sun in the sky!