Firstly I think that younger ones Gambling is very wrong. The age restriction for Gambling is more like a safe guard to prevent unnecessary and irresponsible Gambling habits of an individual and hence the Gambling restriction of 18+. A lot of teenagers are not able to make proper decisions for themselves hence if they are given the opportunity to gamble they will end up abusing it and even harming themselves. One common issue is that in some countries they are unable to properly enforce the 18+ Gambling rule hence alot of these teenagers in such countries are able to do such things illegally.
It's worse than you think. Those kids are not gonna quit even if someone talks to them about the damage it's doing to them since they were already exposed to it earlier. It'd be hard to break off such habit now if they're already doing it with their uniforms on? That's really wild. They now have their balls deep in gambling. Whatever you learn in your teen days, is gonna stick with you in life for sure. That's why I fear for those kids especially if they randomly win, the dopamine hit will push them to bet more.
If we talk logically then it is clear that it is no longer appropriate for children to carry out gambling activities, because if it is just small game that is played with their friends in school can be considered as their entertainment.
Just imagine that they are still school children and whether they deliberately don't go to school or after school going to betting shop is not normal thing for school children to do, I sure if their parents found out they would definitely be very angry.
What is really unfortunate about something like this is the bad impact that could happen to them, such as gambling addiction, losing direction in learning, losing excessive money and the potential for things that go beyond the limit to the loss of child future.
They gamble without any control or proper basis so that they can easily get all the bad effects, betting places should have an age limit for being able to enter.
But basically things like this are happening lot now, even where I live there are several similar incidents, it will be very difficult to suppress or prevent incidents like this.