As for me I think the parents owe the children nothing to explain to them as long as they never let the vacuum of their responsibilities in training the children remain void, when your children never have access to gambling or where they do such then you owe them no explanation, parents have their own part they play from their children way of upbringings, they must not engage doing things that we will not be aware of which may affect them in life the wrong way.
Parenting comes with a lot of work and educating the child on the danger of some action goes a long way to saving the child in the future when they are no longer with their parents, and it doesn't necessarily need that the child is exposed to it before you give them the awareness on the dangers available in the society and how to handle them.
I use my personal experience to check this thing, when I was young, my parents use to tell me real-life stories and sometimes we had both the good the bad and the ugly so those lessons thought us how to handle some in our real life.
Gambling lessons should be thought to young kids so that that knowledge will help to guide their actions when they grow up.
We need to safe ourselves from future challenges by avoiding our children get exposed to gambling right from onset, children are not yet responsible for their school fees payment, neither do they have other responsibilities attached to them to take care of which needs financial aid, their time is needed to be invested on their education and learn about other careers in life than getting too exposed to gambling at their early stage.