When the hero boy rides the Polar Express, the conductor has the same voice as the adult version of the boy. Did the conductor go back in time, and bring his child self to the North Pole?
No, this is just the effect of Tom Hanks doing a number of voice roles for the movie...
Tom Hanks voiced the Hero Boy's father, the Conductor, the Hobo, Scrooge, Santa Claus, and the Narrator.
There is no suggestion that these are the same characters moving in time. In essence, the Narrator is telling his own story and, for the major adult roles, using his own voice as theirs.