"First, in your example of a birth certificate, where are you going to post it on the parents' side? You can't post the child's birth to the parent's birth, can you?"
/*Why would you want to document the birth of someone in someone else's record? The relationship of "child" is a secondary effect of the event of a birth. Documenting both a birth and a child relationship would be duplicative.*/
"If a couple had 16 children and you found 3 from here and 4 from there and 2 are unknown by name and 6 are from over over yonder - and 14 of them may have come from any of four different wives - who do you distinguish all of the sources for EACH of the 16 children - in both the CHILD's and the PARENTS's record?"
/* No, not in both. What ever source you have from which you conclude Mary is a child of John, no matter how many other kids there are, I would put in Mary's birth fact. Why? If you have evidence Mary is a child of John, then it is evidence Mary was born = birth => source-cite how you know that birth happened (and when if there is evidence of the date). The program or chart or whatever you are using to record your findings connect the two/three people together.*/
"What about a CA death certificate, which often only gave the deceased person's parents surnames? If a man, that generally give a surname to his mother - but which wife of the father? If a woman, this gives her maiden name (surname of father) and maiden name of mother - but who are her mother's parents and which wife of the father is she?"
/*(no idea what the point of that was.)*/
"Or a headstone, which gives a middle name that suggests "almost certainly" a maiden name - and that's all you have - or contrary-wise you have 20 other sources for her, none of which gave her maiden name?"
/*(again, no idea what the point of that was. How does that tie to "where to show a relationship of child-parent?)*/
"Or, in the case of trying to corroborate a 1700 (ie before censuses) published genealogy, all you have to corroborate her identity given in that Genealogy is that her asserted parents are, indeed, buried in the same plot with her?"
/*(wow, I am getting lost.) If you are taking that "published genealogy" as your source, then, ummm...it is the source evidence of a birth, i.e., a child. I would not do that unless it was professional genealogist work available for inspection; even then, it would include sources, so it would be better to use those, if possible.
Wait, you said 'corroborate a published genealogy.' As I said, I am lost. If you are saying the published work assigned Mary as a child of John because she was buried in same plot as John as well as another person--the wife/mother, how would you know it was not John and 1st and second wives? We are way off track from the fundamental issue I fear.*/