Btw, despite gambling, parents do all kind of activities that are inappropriate for underaged. Do you think kids really focus on all of them? Example. We dont let kids use sharp objects like knifes or scissors. The damage they can do with it is immediate (not just a possibility like gambling addiction). However they see us using them, but they dont focus on them, nor show a huge passion to use them. Moreover, if a kid is a girl, we even push or ask her to help to cook, to slice something and etc. We even teach them to use it when they are very young and give them toy kitchen as a toy to play with plastic knifes and etc. Then where is logic here? From very young age we teach them to use dangerous objects.
If we continue your thought, then children should simply be taught how to play gambling games correctly and benefit from it, similar to scissors used in everyday life or a knife used to cook dinner?
I would only add one condition: that children should look for/earn money for gambling on their own.

To succeed in any business, you need to start learning it from an early age. Look at any sports champion - they all do it from an early age. Therefore, to earn millions in gambling, you need to start doing it from childhood, to gain huge experience and develop skills.

P.S. Just in case, I am against children's gambling (children should not be allowed to those types of activities in which most adults are losers) and this is just a light joke.
Nope, my thought was different. From just seeing someone gamble, or giving a little try, or having an explanation what gambling is, nothing really bad wont happen. If parents do it none stop, than yes, there will be consequences. Better teach kids that gambling is for fun, not for money making, and show examples how they really can earn, and there will be much fewer problems.