Board Thread:Spoilers!/@comment-26159109-20160119214649/@comment-1916997-20160321181005

8Rob wrote: I have to rewatch the scene but I think the deal was made with Rumple and Milah's second born child.

This baby is Rumple and Belle's first born child

So, maybe it doesn't apply The way Rumple explained it to Milah it did sound like it had to be their next child, but based on how Rumple acted after that, he must of promissed his next child, thus why having a baby with Cora or Belle would be problematic.