How could a BABY become a character?
Let's assume Rebecca lives long enough to give birth in episode 3, and Clem (along with the remaining survivors) becomes its caretaker. What kind of story mileage could Telltale get out of a baby? I mean, as a general rule of thumb, babies don't have much of a personality besides needing and wanting.
But here's a much scarier question: How long could a baby last in the midst of a zombie apocalypse? Considering we still have no clue what happened to Christa's child, we can only assume the odds are not good.