Gambling companies have a responsibility to protect children and gambling addicts. They should not advertise on posters in poor towns and villages because people there have money problems. If they advertise in rich cities they should avoid schools and youth clubs. Gambling ads are a part of daily life for people who do not want to gamble.
You are absolutely right, and I would even add that gambling establishments should not only not place their advertising, but moreover, they should prevent even the slightest chance that children from poor cities or villages can become addicted gamblers. And this should be achieved by the fact that schools in such regions should conduct additional courses after school, at least for a few minutes, where the teacher will at least briefly talk about the harmful effects of online casinos or sports betting on immature minds.
Though it should be a obligation of the person itself but it's going to be helpful if casino campany will prevent placing their ads where young kids will see them clearly, like posting irresponsibly they should take this as sole responsibilities though government should also accompany them providing right guidance, similar to what you mentioned, school can take extra time to provide proper information giving their students deeper ideas if what's await to those who will going to get addicted.