Having baby with Sim in different household spawns extra child in said household

My household female (alien) tried for a baby and had a baby with a fairy from a different household. She married him, and declined to move him in. I noticed an infant in the fairies household that I didnt create (I had just created the fairy family specifically to have my alien marry the boy eventually). I checked the family tree and it said it is my Aliens (female) and the Fairy (male) child. This child looks like neither parent but is theirs according to the family tree. Both household have adoption turned off, so the only way they should be able to have children even if im not actively on the household is physically, and my male fairy never got pregnant. 

I have no mods or CC.

Edit By Crinrict: Adjusted Title