If the teens are still under their parent's care, parents I think should have the right to know what their kids are doing online and on their phones. Whether privacy is an issue or not, my teenager will definitely be under martial law and I will check their apps and browsing history.
Teens are yet not fully aware of what they are doing just as Colby Cotrone said, they are fans of the sport but they are crossing the line already when they gamble. Government agencies may step in if it becomes an epidemic already. Australian government AFAIK is doing lots of things to prevent their citizen from gambling including banning ads everywhere.
You are right but the problem is that many parents have no idea how to control the smartphone of their kids, at least in my country parents have no idea about many things that's related to modern technology. Almost 99% of parents don't know that their daughters post naughty pictures on Instagram, run onlyfans and do some other nasty stuff.
At my school, it was very popular to play slots and make sports bets, you were kind of cool if you were doing this. Parents had no idea about that because parents didn't know the functionality of smartphones and computers well. This problem might be fixed in young parents today. When I was a kid, you could scan the ID of your parent and create an account on their name. Then there was always someone who had an account and card from a young adult and they were cashing out money through them (account-to-account transfer).