Elderling Creations Theory (Spoilers through all the books and Dragon Haven)

['thul]

It is common knowledge that Elderlings can have children. Tintaglia said so in the liveship books. 'thul's theory around inability of having children ranges around those that are neither human nor elderling, but in transition in between. More about it within spoiler.

Spoiler

These beings agree that those touched by the rain wilds are partial elderlings. most of them are no more than a few percent, though.
The presumption that elderlings of the stage Reyn/Malta is at cannot have viable children comes from the fact that Tarman had to help it remain alive. As for why tarman knew that? Thats fairly simple... Not even close to all the old era elderlings were born that way. thus it would be natural dragon knowledge that elderlings of certain stages cannot produce live children. In early stages (Jerd, DH), the child becomes more serpent than dragon than human.

These beings believe that in fully changed Elderlings, their reproductive systems have changed sufficiently to reflect dragon tendencies. Where humans can (relatively) easily become pregnant, long-lived races do not have quite so easy a task of it. Dragons have to wait over a decade after cocooning before they can lay eggs. Thus it would stand to reason that fully changed Elderlings simply have to work harder at becoming pregnant, but once pregnant and within reach of dragonkind, the children should be viable most of the time.
Before they are fully formed, Elderling bodies are still in transition. Since the changes are on the genetic level, the DNA of a transitioning Elderling/human is unstable. When DNA is unstable, it is hard for the body to replicate it, since one strand might not be the same just a few days later.
One thing 'thul do wonder about is how long the periods of gestation are in Elderlings and dragons. Obviously eggs aren't laid instantly after mating. Considering how suddenly Malta's birthing came upon her and how (relatively) easy it was, the period of gestation is probably shorter than it is for humans. Shorter gestation typically means smaller infants. The potential presence of claws also supports this as a good idea.