Bridge to Terabithia by Katherine Paterson

Bridge to Terabithia
192 pages; HarperCollins
When Leslie Burke moves next door to Jess Aarons, he finds that she loves to run as much as he does, and the two become friends. Together, they create a secret kingdom in nearby woods and name it Terabithia. There they rule, fight giants, share stories and seek solace from the everyday world until tragedy strikes.