so it seems the best thing we can do is to warn them about the dangers of gambling at such an early age and hope they listen to you and do not gamble until they are old enough to understand what they are doing.
For the children who already know about gambling, yes that way seems good for them. But we must ensure that they really understand what we warn or advise to them. As they are still at a young age, they may have difficulties to understand the warning.
However, the best way is not "warn" them. But how to make them don't know about gambling. Keep away from them all things related to gambling. So, we don't need to warn them because they don't know about gambling.