When we talk about minors not being allowed to gamble, it's a general rule everywhere, not just in some countries, so if a child who is below 18 years has been gambling without the knowledge of the parent and he or she happensto win an amount which requires advanced KYC to be passed, if the child uses his real ID card, it will be noticed that he's not yet of age.
I think I was generations pass societal values 10 to decline gradually. And as a result of this many parents would accept that especially if the amount they want from the castle one is really really huge compared to the financial state of the family. Anyways it is never a good option to allow kids gamble and this doesn't need much of an explanation simply because the effects are obvious on the society. Kids can slip into addiction super fast and a kid consumed by any form of negative addiction is the last thing you'd ever want as a parent.