I suspect that Ben has become the adoptive father to kidnapped Alex. It is hard to believe that Danielle knew exactly who he was when she captured Ben in the net and handed him over to the Losties. I think if she had known he was the father to her lost child foster or otherwise she would have tried to make him return her to him. (unless, she was part of the plan to get Ben into the losties camp??) I also suspect that Alex is very bright and has figured out that she does not belong there, but was taken. That is why she helped Claire escape with the baby, and seems to be fighting against the others in everything that she can.