They don't respect that, they just put it there so the authorities can see that they're not breaking the law, kind of like adult content on the Internet, they don't really enforce that minimum age requirement, they just put it there so they're compliant with the standard of the government. These aren't any measure to prevent underage gambling, more like a shield so the business can go smoothly as it can be.

If I'm being honest, the only effective way to make sure that underage gambling doesn't happen is that the parents of those children do an intervention, making sure that they're in a loving home and their needs are met and the proper values are being instilled in the child, I believe that's how you prevent underage gambling. Telling them what they can't do and the consequences of doing those don'ts are a good thing too but most children doesn't understand consequences until it's too late so this one is a second option.