What does it matter if Derek has a baby? I mean, there's no way to change the "plot" now anyway. I think it was just a mess-up by someone who understood a tweet wrong, but just imagine it. Derek Hale. Holding a baby. BTS Tyler Hoechlin playing with that baby. Stiles fuzzing around the baby. We need to look positively at those weird, twisted, bizarre possibilities.
You know why it matters, but even so, again, leave that for fanfic. Derek can have all the babies he wants in the appreciative hands of the fans. Not the vindictive paws of these writers.