I don't think that "Starbuck's baby" is actually part cylon. Remember what Adama said about that model always lying. I think the child may be from Starbuck's missing ovary, but they inseminated it with another human.
That could be or the opposite could be true and she is in fact 100% cylon, and is either a new model, or one of the models we haven't seen yet. There are 12 models and if my count is correct we only know who 7 of them are, there's Number Six, Sharon, Doral, Brother Cavil, Simon, Leoben, and D'Anna Biers. For all we know Leoben is just frackin (had to say it) with Kara, and is using the child to break her.