My parents did something similar for me, and I still remember the lesson a few decades later.

I think the details matter here. If you give your child $10 every month to make one bet, sometimes they win, sometimes they lose; you are doing it wrong. If you give them $50 and let them make a series of bets not exceeding $10, they will learn that the curve sometimes goes up, sometimes goes down, but ultimately ends up at zero. Not because "you were not lucky today, but maybe the next time", but because this is how the system works.