Everyone -at least the non-hunter people- assumed that Dean and Cas had adopted their daughter Mary, because really what other choice do partners have? Well, Dean and Cas had one other. On a case about a coven of witches Cas got hit with a gender swapping spell. He was trying to save Dean from a spell cast by a witch by jumping in front of him, that's when he was hit. Being a celestial being, and therefore not having a designated sex, didn't seem to matter because it switched the gender of his vessel Jimmy Novak. Dean just stood there in shock watching Cas' features become feminine , leaving Sam to deal with the witch alone. It didn't really matter, though, because the amount of power used in the gender spell was all she had. Dean finally accepts that he loves Cas and a month later, they find out that they are having a baby girl, Mary. Cas, of course, opted to wait the year for it to wear off, and Mary was born. They kept moving around and didn't settle down until Cas turned back, but I digress… Sam was sitting in the living room of the family farm, waiting for Dean to get back with the beer so they could watch the big game between Texas and Texas Tech. Mary was sitting on his shoulders, brushing his hair and putting it in braids and ponytails. Once she was done she threw her arms around Sam's neck and said, "You're my favorite Uncle!"
Sam , of course, chuckled a bit at this and told Mary, "I'm you're only Uncle silly." Just at that moment the door opened and all of the sudden bottles shattered against hard wood floor.
"FUCK!" He yelled, "We forgot Adam!" And that, friends, is how my niece started the hunt to get me out of Hell, and the cage...
A/N: Dean is referred to by Mary as "Daddy" Cas is "Goaal" it is Enochian for Creator or Father.