I don't understand how you guys think we'll ever know who the father is. They're both Korean, and Jae was sleeping with Sun we know, and Jin obviously was. So it was either she got pregnant from Jae, or Jin's bad sperms got cured by the island, either way I don't think there's going to be a proper way to introduce it through the show. Unless it's going to be like that episode of the simpsons where it shows Homer's sperm just floating around bumping into each other!