You'd been friends with Sam and Dean for a while. You were a young angel and didn't necessarily always fight in the war. So Sam and Dean let you stay with them. You were pretty clueless about a lot of human things but you learned fast
Right now you were watching some TV with Sam. He always let you watch cartoons. He usually just babysat you and didnt have to pay too much mind if you were occupied with the cartoons. He was nearly asleep when you found yourself learning a new word. DAD
On the show the animted kids started to explain what dads were and it reminded you a lot of Sam. You repeated after them on the tv almost like a baby. And then the kids started talking to their dads. You decide to talk to Sam.
"Dad?"
He thought maybe he was dreaming or something. He felt a bit shocked. Maybe you were just repeatinf after the show. He shut his eyes again