Gambling ads on tv are not regulated, most especially, if you are subscribed to a cable tv, or internet TV like YouTube and others, there is a high chance that such ads, or even something worst, might come up from time to time.
The only solution to this I think is to get the children their own TV, where they can comfortably watch cartoons and other children programs in their room, by this way, the children will begin to see less gambling advertisement ads on TV when their parent are watching a sports program.
If children have access to TV and the internet without limitation, they'll likely come across these gambling advertisements. Nowadays, with plenty of sources of entertainment online, it's too risky for our children to give them full freedom. It's still up to us how to discipline them and provide only what is necessary at their young age. We want our kids to have the same interests as us, if we love sports, we might also want them to enjoy sports. However, gambling is just quite different. This thing is what we call for adults only or mature content, similar to porn shows, with a warning: not for kids.
The world today is totally uncontrollable because the internet and the TV makes it so easy for children to access these things online and moreover advertising of betting or gambling sites are done on a more wider scale now and even the internet like social media are filled with these kinds of advert too but if the parents of a child keeps a close eye on the child then I think it's avoided and moreover there is always parental guidance rating on some specific TV shows and even the cartoon themselves.