Speaking at the Develop Conference in Brighton today, 2K Boston’s Ken Levine said that moral choice was somthing which came later in the development of the game.

Levine explained that although the game did start with the idea of both protective characters and gatherer characters, only the Big Daddy concept was retained. It was also revealed that the gatherers, didn’t become Little Sisters until later, having originally taken the form of worm-like creatures. Once the gatherers became little sisters, this is when the moral choice was created for gamers to make. 

"We ended up with a game where we had to confront this moral choice, rather than setting out to create that choice," explained Levine.