My Au-ish series headcanon.
Dean: We got a case, werewolf, upstate, Garth called so we gotta go now, so you’re babysitting
Castiel: What? Dean, I do not know how to care for children
Dean: It’s about time you learnt like Sam and I did, Cas, what’s she gonna do? fly away?
Castiel: she’s half angel, Dean, she could very well, fledglings can learn things pretty quickly
Dean: well it’s not MY fault you left me a present in purgatory when you still had wings, you’ll be fine, get to know her or something, do fun father-daughter, angel-fledging bonding or something
Castiel:…. can I have Charlie’s number for emergencies?
In which Dean and Cas have domestic Daddy disputes while Sam plays with his niece Faith Mary Winchester.