The idea of pocket money is usually that kids can spend it on what they want. That includes sweets. Although of course parents can say "no" - but that goes for virtual items, too.

Teaching kids to gamble - I would see it as the opposite, teaching them not to gamble. They will be confronted with gambling opportunities all through their lives, with higher stakes. Better to learn with pocket money.

Here in Germany afaik there is also a law that children are not able to do business transactions. That means if you sell something to a kid, the parents can come back to you and say the transaction is invalid. I wonder how that works out with virtual goods and games?