Complex sentence: The family then moved again to the North Hollywood section of Los Angeles where Ladd became a high school swimming and diving champion and participated in high school dramatics at North Hollywood High School, including the role of "Koko" in "The Mikado".
Split into simpler sentences: The family then moved again to the North Hollywood section of Los Angeles where Ladd attended North Hollywood high School. He became a high school swimming and diving champion and participated in high school dramatics, including the role of "Koko" in "The Mikado".