If you forbid something to a kid then kid will find that even more attractive. Forbidding anything will have contra effects in most situations.
I believe people hear many bad stories about gambling generally, sometimes with family members involved, that's always makes situation more complicated.
I'm not affected by any of this stories because I started to gamble with sports betting with friends from soccer, more seriously gambling came after. I build my way alone, and I know how to handle with gambling. Its something you need to learn. When we are about that its important for very life aspect you can think off, you need to know how to handle with good and bad times, and to not let something to lead you in crash or disaster of any kind. Gambling is special because you can climb fast, but you can fall even faster, don't fool yourself its like that in everything just time for climbing and falling is different.
Learn kids how to control their emotions and how to properly decide what is good and what is bad, if you try with forbidding kids will try to find a way to skip your bans and to try that sweet forbidden things.
If you do not forbid it anyway and keep quiet about it, the kid will still find it attractive if he or she wants to. However, it is better to forbid it in a wise way than not to forbid it at all. A lot of people have forbidden things without even explaining why it is wrong. Paint a very bad picture of what gambling does to a kid, and you will surprise it would never leave their head for the rest of their life.
I remember how my dad used to tell me how my granddad ruined his life from being a wealthy man to a pauper as a result of gambling. That shit stuck. Gambling itself is not usually the problem anyway, it is always us and most times, those who are greedy naturally are always the ones who usually end up falling into the trap of addiction when it comes to gambling.
Family past incidents will always play an effect in the minds of those who may want to consider gambling since they could have seen some family members that gambling has had an adverse effect on before and hence use that in their own decision making when it comes to gambling.