I would want BOTH of the children. I know that it is not realistic or fair but that is how I would feel.
My blood is my blood and the likkle pickney weh me raise for 11 years is my child, too. How can you not be with both of them?
On TV the parents would move into a big house and raise both kids together, but in real life there would just be pain. The best thing would probably be to keep the child that you raised and develop a relationship with your "real" child. And have the kids spend time at their bio parents home until they got used to them. And then maybe switch after? I don't know.
Hopefully both families live close because I think both would have to come to an agreement to share them as I imagine it will be equally stressfull for the children involved. Only way a child jumping at that opportunity to go with a different family is if they hate their parents, being abused, or wayward and see an opportunity to get away from the parents that trying to keep them in line.