I know some will be thinking about it, but before someone brings it up...Since uploading this image, the artist has commented on the subject (at least on Facebook) in regards to Eila and Sanya having children...
"The story here is that Ilmatar granted them the ability to conceive through her magic." (http://tinyurl.com/dyk2wbw)
I know the answer seems fairly obvious, if you follow the show, but I just wanted to leave this here anyway.