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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.
I can't agree more! Indeed, visual explanation is better for most kids than a million words. Maybe going to those places where many people are playing slots simultaneously and showing your kid how most of them look like, their faces distorted by greed, and your will never want to be like them. But avoid showing him their faces when they win because he will most likely
want to be like them. If that happens, try to explain to your kid that the chance of that is very small, and it's not worth it to risk turning into the people he saw earlier who were playing slots. Why is the chance of turning into them is high is because he's a kid, and before certain age he won't know how to treat gambling properly.