You could do that, but it seems kind of obvious and condescending? Cause right now you can forbid it and theyll see all their friends lose money and never win anything until your child is of legal age. For everyone else, it seems like some kind of inherited cultural addiction that gets culturally passed down. Just openly mock gambling as evil/a scam/rigged and they'll probably be more likely to pick that up if you back with principals instead of taking the weak, confusing, and contradicting stance of feeding $50 into the evil system.