The tone of this book is made to sound like that of a 12-year old boy. Since the story is told from the point of view of Percy, a 12-year old boy, the tone of the story reflects it. The author takes a more childish view on the world of the gods to make it more appealing to children. For example, characters in the book can be very humerous, but I wouldn't expect the god of the underworld would be very comical in real life. The tone of the story really adds some humour to the book and makes it a little bit more laid back than if it was told from an adult's perspective.