I think it is important to teach teenagers and children the Value of money and how it needs to be respected, How to avoid becoming addicted to any form of Gambling, whether it is Poker, Blackjack, or anything else that may come their way.
Being responsible for their own Money no matter how much pocket money they get, and the perils of losing it, There is no point beating them in a game of Blackjack, and then giving them the money back that they lose, By all means return it, but make them work for it, even if it means Making their beds or washing a few Pots and Pans etc.
Teaching them that if they lose money gambling, it is not that easy to get back, is a more positive approach than taking all their Sweetie Money and giving it back without a cost, is giving out the wrong message. Gambling can be Fun, but teach them the risk's and negatives along with the Fun part.
I taught my Daughter how to play Blackjack before she went to Kindergarten, not so she could gamble but it taught her how to count from a very early age, and when she got older and started going out to Parties with her friends, if she got into a friendly game of cards, she knew what to expect and knew enough about the game to beat her opponents.
She is now in her Forties and still can feel comfortable gambling for fun!