In the beginning, there were no rules against sin in fact until Adam sinned he and his wife was doing just as G-d had commanded them, going forth and multiplying. The children learned from their parents they were naked and did not know it?!? The rest you should be able to piece together.
It isn’t until the fall that the clock starts towards the redemption of man. It is then G-d tells Eve she will have an increase of pain in her childbearing.
Genesis 3:16 Unto the woman he said, I will greatly multiply thy sorrow and thy conception; in sorrow thou shalt bring forth children; and thy desire shall be to thy husband, and he shall rule over thee.
How long were they all copulating before the fall is the question? The answer: long enough to know by Genesis 4:17 there was enough to build a city and for Cain to marry.
When G-d cursed the whole earth for the sake of man it included the offspring before the fall who were indeed part of the earth. With the clock started on man everything we learn is after the fall and the redemption begins with the two sons Cain and Abel.
The devil did not respect the offering Abel made, but in the end, I think he will.
Abel is a biblical first name which may derive from the Hebrew Hebel, itself derived from hevel (breath or vapour), or from the Assyrian for son. ~ wikiwand
FYI Mom and Dad did not have belly buttons.