A picture is worth 100 words (adjusted for inflation).

Here is the Corleone return to Sicily circa 1923. Michael, then 4 years old is standing in front of Vito. Fredo, then 5 years old is standing in front of Don Tommasino in the wheelchair. Sonny, 7 years old is on the left and the infant Connie is being held by Mama Corleone.