If we talk about cash,.then it is obvious it would become more difficult to control. Nothing stops a group of teens with cash on their hands from gambling their parents money away and not getting caught.
Are you talking about offline casinos? And being a licensed casinos, not a shady ones? They I would say that those teens with cash in their hands gambling career would end at the entrance of the casino, as guards wont let them gamble. I think not a single casino would want to risk their reputation and licenses in exchange for lunch money. But, nothing stops those teens from gambling between themselves. Play cards are in free access, and they can place bets on different scenarios between themselves.
Or online. Lunch money will be taken from them by the online casino and they can always fake their ID's there if KYC is needed. Or, just one adult friend can lend his account in exchange for an interest out of the bets that will be made.
Also, there are online casinos that are not doing KYC unless you hit a certain amount which will make you questionable about your deposits and withdrawals. So, there's always a way for these teens to gamble and just using Google will provide them the answers. This is why concerns are growing with them and I am also concerned with my kids' future after witnessing how easy it is to gamble now. Sometimes an e-mail address will suffice to gamble. Scary.