Removed this because it was first person thread mode and had no source. It shouldn't be put back until the source is found and named.
(I heard this on a radio program, but it was probably adapted from a short story:) A soldier from WW 2 or maybe the Korean War is mentally sent back to his childhood, possibly due to being in a coma à la Life On Mars. Once he convinces his dad this isn't just a kid being overly imaginative or brain-damaged, the son plans for their future by picking stock options and things to bet on, as well as preparing for the war ahead. The son reverts back to being a child when the soldier comes out of his coma or dies, and the father has a safe full of sure things.
I've read the story. It was part of an anthology... somewhere.