Why does Richard set the house on fire?

Richard has been platying with fire out of boredom..... he's only fours years old. None-the-less, he begins by lighting straw from the broom in the fireplace, and graduates to setting off the curtains just to see what they'll look like while burning. He was curious..... the fire was an accident. In this case..... you have to wonder why a four year old has been left alone.