GIRL
I would adore seeing Dean with a baby girl. He’d be incredibly attached from the second they said, “It’s a girl.” making sure she was well taken care of. She’s his little princess and she would be his entire world. Dean would have stars in his eyes, counting down the days and when she’s born he’ll be smitten from the second she’s placed in his arms. He’d watch her grow, keep a close protective watch on her. Seriously boys, don’t mess with a Winchester’s daughter. He’s got guns and he’s not afraid to use them.

BOY
A lot of the same characteristics during pregnancy as the girl… only slightly different. See, I imagine he would find himself cruising the toy aisles a lot, excited to have someone to play with. He never had a childhood himself so he’d be excited to give his own son the life he never had. Teaching him things like the workings of a car engine and getting smacked for teaching him curse words and laughing about it. Like his own little buddy, living vicariously though his son’s life.