Complex sentence: The story begins when Claudia Kincaid, an 11-year-old girl, the oldest of four siblings (the others are all brothers), decides to run away from home because she thinks her parents do not appreciate her.
Split into simpler sentences: The story begins when 11-year-old Claudia Kincaid decides to run away from home. She is the oldest of four children, a girl with three brothers, who thinks her parents do not appreciate her.