Love the thread, not for the results as much that it re-confirms my long held belief that achieving behavioral changes in humans is almost impossible.
I still have a decade or so before I have this issue with my kiddo, but I will likely first make a game out of it for a few years, then likely let him run a paper portfolio for a couple more years and then seed his real-world portfolio.
What will come earlier is building up the prerequisite trait of saving habitually. I guess I might begin with "here is your weekly allowance - in two bills - go put one in your piggy bank" and take it from there. If anyone has any tips on this part, I'd love to hear them!