Maybe gambling is legal in that country so the betting shop owners don't forbid them from coming to gamble but unfortunately by wearing school uniforms to gamble we can conclude that they seem to prioritize gambling over their school lessons, in contrast to countries that prohibit gambling like in the country where I live. Maybe If a student comes to a betting shop and wears a school uniform, he will definitely be expelled from school as a sanction for his actions in order to ensure that the university's name is not tarnished among the community.
Even if gambling is legal in the country, there should be the limitation about the ages. In most countries, the minimum age is 18. If the students aren't in university level yet, they shouldn't go to gambling places. Since OP stated they were wearing uniforms, I guess they are the students of Junior or Senior high school. Ideally, the students should be not allowed to gamble in the betting shop.
Yep, I support the idea to give the sanctions to every student who go to gambling shops, specifically those who wear uniforms. The students possibly don't only break the age limitation in gambling, they also ruins the school's good name because there should be the identity of the school in the uniforms. Also, the government also need to cooperate with the betting/gambling shops to refuse the students with uniforms and the underage visitors. If the shops allow students and the underage visitors, the authority must give the sanction to the betting/gambling shops, too.
*
Information about age limitation: https://en.wikipedia.org/wiki/Gambling_age