Complex sentence: Fowles spent his childhood attended by his mother and by his cousin Peggy Fowles, 18 years old at the time of his birth, who was his nursemaid and close companion for ten years.
Split into simpler sentences: Fowles spent his childhood attended by his mother and by his cousin Peggy Fowles, 18 years old at the time of his birth. She was his nursemaid and close companion for ten years.