This is one disadvantage but how can we be sure of it that many of them are gambling? I doubt it that there's ample of them, they don't even know how to buy bitcoin and they can't even buy bitcoin because they are minors and don't have something for living.
This is a minimal case but I'm not confident of it as well because many or less, they are still minors that should have been guided by their parents.
Minors are probably going to learn about Bitcoin way easier than we did - they represent the new generation, most of them were born post Bitcoin's existence. Kids don't have a monthly wage but they do have their ways to get their BTC for free *cough*
parents' credit cards *cough*
I think the number of minors gambling online and using services that are supposed to be for adults only is quite large. Best example is the fact that most replies on YouTube channels that are supposed to be for a 15+ audience are written by kids (for proof, just take a look at any kind of meeting of YouTubers and their fans).
As a parent, it gets harder to control what your kid does the more tech advances. A kid is curious, so it's quite obvious that there'll be a time when that kid will want to try out what they're supposed not to. Moreover, most of them are addicted to gaming so they'll want some bucks to get games with - do you really think kids know what money means? Because for most of them it's just a number that goes down when you buy games