Well... Since the heathens shouldn't have any babies anyway, it's not unlikely that they will hang on to them. There is no mechanism for counting down until they become two years old, or for producing new little heathens. You can't see any timer since heathens can't be selected.

My guess is that you'll have to wait until they're converted. I wouldn't be surprised if the babies disappeared then, although I suppose they might be carried forward (though the clock would probably only start counting down from when they convert). Xay says they have seen this before, so perhaps she knows.