Among other things, lots of those kids are probably using their phones to gamble way more money than they'll ever lose playing poker with their friends.

Playing poker with friends is at worst zero-sum with limited downside; your friends will probably cut you off when you run out of money and the money stays in your little pool. Betting sports against a faceless profit-maximizing corporation is negative-sum and if it turns into a problem for they're happy to raise your minimum and encourage dumber bets.