~ Younger ones doesn't have to gamble and with supervision from their parents, younger ones will not trying to playing gambling. If their parents can explain the effect of playing gambling at their ages and what will happens to people around them, their children will not trying to risks themselves by playing gambling. They will be careful when they are with their friends and always reminds each other not to playing gambling. They will tells many things about gambling, especially if their childrens can explain every details about the effect of playing gambling.
I think it's extremely hard to explain to young children of the age below 12 why is it bad for them to gamble. First off, you have to be an authority for your kids so that they were trusting your words. Secondly, they may simply don't get what you are talking about.
At that age the best explanation is still a visual explanation. Maybe trying to show a regular gambler at small local casino, and a successful person in expensive car near business center or offices would do the job. The more facts of how gamblers lose money and conditions they live in comparison to others you provide, the better it would be. Find out what kids at that age use to measure success, and use it as instrument to show success. Perhaps, showing that gambler use not expensive android phones, but other successful person uses iPhone 15 Plus would help younger to evaluate who has more money, and who not.