That may be so, but we have no specific examples of it. (By the way, 'fecundity' is the word we should be using not 'fertility.' Fecundity refers to the actual number of children produced, wheres fertility merely refers to the ability to produce them).

: Elrond and Celebrian had three children.

Precisely my point. What I am basically suggesting is that the Keepers of the Three used their Rings (in the Third Age) in slightly different ways, thus acheiving ends that they themselves found desirable. Gandalf used Narya to "rekindle hearts to the valour of old in world that grows chill." Galadriel used Nenya to slow the fading in such a way as to make Lorien a sort of living echo of the Eldar Days. As Tolkien says: "In Rivendell there was a memory of ancient things; in Lorien the ancient things still lived on in the waking world ..." But Elrond, I suggest, used Vilya to not merely slow but actually to defy the fading, by perpetuating his line. And ensuring that the bloodline of the Elder Kings flowed on into the Age of Men.

I guess, we could say, that Galadriel's use of Nenya was backward looking (to the Eldar days); Gandalf's use of Narya was present-oriented (to fight the war against Sauron); and Elrond's use of Vilya was forward looking (What are we Eldar going to leave behind when this whole Ring Business is over with?)

As for Legolas ... well, as I said, we don't know when he was born, and it is best, I think, to leave it at that.