There's a baby, but neither Sam nor Dean looks very pleased at its appearance. Word is Darkness will take on the form of a specific entity, and a she to boot. Could it start out as a baby, and this one in particular? That wouldn't be a reason to smile.
It's Sam! How we've missed you, Sam. The brothers will be up against the Darkness, a pre-biblical foe who was defeated by God years ago. Sam is shown reaching out to God in the trailer. Can he be of help again? You'd think he might be angry the Winchesters released Darkness after it's already been banished.
Crowley likes to talk to young men in pairs, apparently. When the Winchester brothers aren't around, he'll find another pair of young men to take their place! What do you think he knows about the Darkness? Was she ever mentioned in his social circles?
Castiel: It's very complex. If the pizza man truly loves this babysitter, why does he keep slapping her rear? Perhaps she has done something wrong. Dean: Are you watching porn? Why? Castiel: It was there. Dean: You don't watch porn in a room full of dudes. And you don't talk about it. Just turn it off. Well now he's got a boner.