Meanings can get lost when you aren't immersed in a culture, yes. But if you want answers, maybe it helps not to ask us, but to ask yourself and your son. IS this supposed to mean something? Why would their father turn into the maize god? Why would the final set of people, the ones the Mayans thought we were descended from, be made of corn? Animals were unsuitable, mud was unsuitable, wood was unsuitable, why is corn the right material for thinking beings? What does that suggest about the value of corn? Or of humans, for that matter?
These hero twins become the sun and moon. Why twins? Is there something special about twins? And what's the purpose of having a sun and moon, from a human-centric perspective? (Can you grow corn without a sun? Remember, also, that one of the earliest methods we had for marking the passage of seasons was with lunar months.)
Of course, if you aren't much enamored with supernatural events, that can make it harder. I feel you. Let's try a secular founding myth.
That example is sort of cheating, because if you're American you already know this story. You know why we tell this story to little kids, and there's an even a snappy moral at the end that doesn't take too much thought to figure out. (An ironic moral, given that this story was made up decades after his death, but there's more than one form of truth.)
But what if you were a Martian, or even an ancient Mayan? What happens? Some kid cuts down a tree and then fesses up to his dad. Okay, well, then what? Who cares? The meaning isn't just in the bare words. (That's another potential problem. If your source for these myths is stripped down to the bare details, you might be missing all the information that makes the stories interesting and meaningful.)