Adults have many responsibilities in dealing with children that children imitate. For example, if someone smokes in front of a child, then later that child may want to smoke secretly, so it is better not to show such negative behavior or bad habits in front of the children. I don't think gambling is bad that divides the regions even visually. Children imitate the situation around them and if he sees gambling going on in front of them he may easily pick up but they should understand that gambling addiction is very bad and gradually he wants to take positive side of it.
If they can control themselves from the effect of gambling, they can playing gambling to have fun. But many people doesn't realizes or not sure about themselves so that makes them gets deeper in gambling without have a chance to quit gambling easily. When someone tempts from gambling, they will not see that's a fast way for them to spends their money especially if they don't have a good control instead they will just thinks that's a way for them to wins much money.
It's better adult people not playing gambling in front of their children if they don't wants their children curious about what they do. Adult people doesn't knows when their children will playing gambling with their friends because their children can do that secretly. Adult people must guided their children carefully and doesn't have to show their gambling activities to their children.