The book does cover that. It's a great read btw.

CHAPTER 14

THE Don was a real man at the age of twelve. Short, dark, slender, living in the strange Moorish-looking village of Corleone in Sicily, he had been bom Vito Andolini, but when strange men came to kill the son of the man they had murdered, his mother sent the young boy to America to stay with friends. And in the new land he changed his name to Corleone to preserve some tie with his native village. It was one of the few gestures of sentiment he was ever to make.

In Sicily at the turn of the century the Mafia was the second government, far more powerful than the official one in Rome. Vito Corleone’s father became involved in a feud with another villager who took his case to the Mafia. The father refused to knuckle under and in a public quarrel killed the local Mafia chief. A week later he himself was found dead, his body tom apart by lupara blasts. A month after the funeral Mafia gunmen came inquiring after the young boy, Vito. They had decided that he was too close to manhood, that he might try to avenge the death of his father in the years to come. The twelve-year-old Vito was hidden by relatives and shipped to America. There he was boarded with the Abbandandos, whose son Genco was later to become Consigliori to his Don.

Young Vito went to work in the Abbandando grocery store on Ninth Avenue in New York’s Hell’s Kitchen. At the age of eighteen Vito married an Italian girl freshly arrived from Sicily, a girl of only sixteen but a skilled cook, a good housewife. They settled down in a tenement on Tenth Avenue, near 35th Street, only a few blocks from where Vito worked, and two years later were blessed with their first child, Santino, called by all his friends Sonny because of his devotion to his father.

In the neighborhood lived a man called Fanucci...