Okay, so God comes down and tells us all that we need to sacrifice our first-born children or the world will end. What are the rules for how this works?

Do you have to sacrifice any kids if the eldest is an adult? Do you only have to sacrifice your adult children if they still live with you? Do you have to hunt down your eldest child?

What if your first-born was given up for adoption, or lives in foster care?

If you adopted, do you have to kill your eldest adopted child? If you adopted and then had a natural child, which one do you have to sacrifice?

If you have children with two partners, do you have to sacrifice a child from both families?

If your partner has an older child from a past relationship, do you still have to sacrifice your own child?

If a man has serial incestuous relations with his many daughters (and his daughters' daughters), does he only sacrifice his eldest daughter, or does he also sacrifice each of his first-born incest children from each daughter?
What if it's a woman with her many sons?

That feeling when you don't believe in God but then you have a power cut at work and you consider going to church on Sunday.

Oooh, I'd love to see that planet.