Why exposing nakedness of your sons and daughters is not mentioned?
I was thinking that Lev 18:6 accounts for that but it does not seem to be the case.
What about Lev 18:17, Lev 18:7, Lev 18:22?
I guess one can use Lev 18:22 as a prohibition of exposing nakedness of your son. But what about a daughter? Lev 18:17 speaks about taking both a woman and her daughter so I do not think it is related to exposing nakedness of your daughter. I am not trying to say that it is allowed of'course, but I was thinking about it and there are two things to consider. First, parents would see the nakedness of their children anyway when they young. And also it seems that God allowed that to create Moabites and Ammonites. Also, Adam and Eve most likely had to procreate through some form of incest...
If one was to have sex with a woman and then she had a daughter (i.e., the man's daughter), then he couldn't have sex with the daughter. The distinction is different regarding the taking of a woman and her daughter/granddaughter when compared with the woman and her sister, because the woman and her sister specifies that it is an issue of both of them being alive, whereas the other does not. Yes, it would apply for one marrying a woman who already had a daughter by someone else, but there's no reason it wouldn't apply if that daughter was one's own.
I did some checking and I think a proper explanation is as follows: Lev 18:6 says that one should not open nakedness of one's kin (shehayr). If you cross-reference it with Lev 18:12,13; Lev 20:19 and Lev 21:2 you will see that this word is defined as your children as well (you son or your daughter). This, I think, would be proper explanation. I am not sure why I was wondering about it before...
I do not think that "opening nakedness" is euphemistic. What about Noah? The best I can agree upon is that it means intentional "opening of nakedness". If it is unintentional or pure (i.e father looking at his infant daughter when handling her) then it is acceptable.
Ammon and Moab were prohibited from joining the assembly on the basis of their egoism (not greeting Hebrews with bread when they left egypt). Not because they practiced incest.
Also I do wonder about Exodus 6:20. It seems to contradict Lev 18:14 and Lev 20:20. Moses and Aaron came out of this relationship.
Same question I have about Abraham and Sarah. They were kin.
Perhaps this happened before the Torah was given. The commands had not been delivered through Moses at that time (Num 15:23), so it is likely not even relevant. There are other things the patriarchs did that would not have been allowed later as well. However, I do believe that Torah is Eternal Law so it is applicable at all times regardless of its knowledge.