Someone just argued with me that gambling can be done by kid too..

I think so. Most of the people who enjoy gamble do not think clearly before they make a bet or play a game, just like the kids. They particularly depend on their luck to play, and that is not what the adult should think. When you are an adult, every decision must be considered carefully in order to avoid the worst situation. And, people who addicted to gambling does not have these factor to become a real adult
in reality, i saw many kids which playing gambling but not for games that on gambling site, but its more like something that they think it is fun to do with their friends and they use money for the kids which is win the games. the kids is only see and do from what adults in around them and they always adopt it and they don't think its a bad thing or good thing, they just do what they see.
It all started with gambling in a little ways, you can gamble with your friends because that is fun but that activity if you do it regularly will turn into a bigger event in your life. People does not usually enjoy when the same thing will be done over in over again, and they will make things to upgrade their gambling activity which might include the use of money.