Keeping children away from gambling is usually the best way, because if children are involved in gambling while they are learning, the future of that child is bleak. Because generally before 18 years of age every child's education is most important for his knowledge acquisition, and gambling addiction is the person who has seen someone gambling before. Because if there is no gambler in your family then there will never be a gambling addict in that family. Because children usually learn politeness first from their parents, and if instead of politeness they get a sense of gambling then that child will definitely show the will to gamble. So I think it is most important to take care of yourself before taking care of children.
When we say that one needs to be emotionally strong and have funds management skills if he want to survive in gambling then it should automatically eliminate the underage and kids from gambling. Gambling needs a mature mind and an underage won't have the mindset to handle the stress in gambling. These skills are crucial because gambling can be highly stressful and financially risky and it is not something for the kids to try out.
They should play other computer games where money is involved but not get themselves engaged in gambling. It's an adult job and that is why most sites will allow only 18+ and verify it through KYC.