In the movie Jack lies and says his mother and father had gone to Santa Fe and when they found a place to stay they were going to send for him. The reality of the situation though was that his mother was killed, and his father was in jail. He also lies about his name as well, his real name being Francis Sullivan.
"Youse guys gotta be Am-bastards!"
Jack Kelly: "Guess I can't be somethin' I ain't."
Dave: "What a scab?"
Jack Kelly: "Naw, smart."