there was an episode of farscape where crichton got to see what his children would look like if he had a baby with the queen of some weird planet (where they had to put a potion on their tongues and then kiss to see if they were genetically compatible).

anyway, i figured it was something similar to that.. six was kind of showing him a hologram of what their baby might look like. not necessarily that they already had a baby, but what it might look like, now they know that a cylon can get pregnant with a human - though can sharon carry to term, i don't know, you would assume so but you can never tell.