Even a kid will eventually get cavities if they don’t brush, and cavities hurt.

Yes, eventually. That's the key word. The whole point is that since the consequence and the action are so far removed from one another, it's easy for a kid to either not care or simply not believe that it's the truth. That's why it's important to have an adult step in and teach them about it before it becomes an issue.

Are you saying all people are children that can’t tell right from wrong without being told?

I am saying some people are like that, I mean, have you ever even met people before? Also to the point, many people are literally children who literally don't have enough life experience to have a grasp of right from wrong and never get there without being explicitly taught in ways they're willing to accept and understand. Your comment here makes me think you're arguing in bad faith.

Sure, but once again, what does this have to do with the Bible and the afterlife? ... If you don’t know what is true, how can you know what is moral?

The part where this connects to the bible and the afterlife is that Jesus attempted to give a compassionate moral framework to people who weren't being taught that by any one at all. He's the Louis Pasteur of the soul and you're speaking as if the knowledge of bacteria was always self evident to anyone who cared to think about it for a minute.

If morality was objective and deterministic the Trolley problem would not exist. Many people simultaneously know what is true and choose to act in an immoral way for their own satisfaction. They often end up wildly successful in doing so as well, just open the news! Morality is completely subjective. For many people being a good person is hard when it feels like it's going against their own self interest and part of being empathetic is understanding this dichotomy. The connection with the bible and the afterlife is a logical attempt to tie self interest back into moral behavior by stating that the reward for it kicks in after death, as it's painfully obvious that moral behavior does not universally feed back into self interest for those of us who are still alive.