Why not? Sex between man and wife is not a sinful thing. It is a beautiful thing. The idea that sinfulness had to exist for people to have the ability to make children is an extremely bizarre one to me. It’s just yet another Mormon belief that makes me feel bad and wrong, like I am reading the worst kind of blasphemy.
wither or not Adam and Eve had a sexual relationship before the fall is pointless. If you can’t have children you can’t have children.
Lehi explained it about as clear as I can find.
2 Nephi 2:
22 And now, behold, if Adam had not transgressed he would not have fallen, but he would have remained in the garden of Eden. And all things which were created must have remained in the same state in which they were after they were created; and they must have remained forever, and had no end.
23 And they would have had no children; wherefore they would have remained in a state of innocence, having no joy, for they knew no misery; doing no good, for they knew no sin.
24 But behold, all things have been done in the wisdom of him who knoweth all things.
25 Adam fell that men might be; and men are, that they might have joy.
26 And the Messiah cometh in the fulness of time, that he may redeem the children of men from the fall. And because that they are redeemed from the fall they have become free forever, knowing good from evil; to act for themselves and not to be acted upon, save it be by the punishment of the law at the great and last day, according to the commandments which God hath given.