The thing though is that they will only have sex at night and I'm not even sure if they'll reproduce when the player is not around.
1.Eh
2.They like it when people watch
I tested in SP creative and they only do it at night, but I didn't test whether they do it when there aren't any players around.
Also, Fiah, are you SURE that they simply dissapeared? They wander around quite a distance.
Edit: Or maybe they do do it doing the day, I see two kid testificates running around.
Edit2: Did you maybe forget to light up the inside of the houses?
Edit3: Anyways, made a nice population explosion in this village.
Edit4: Iron golem just spawned a moment ago.