Coming Down On A Sunny Day (http://archiveofourown.org/works/2276331/chapters/5002224) by maychorian. It's also on FF.net but the author's name is lauraofmaychoria.
Summary: In 2009, Castiel watches the Apocalypse end disastrously and makes a decision. In 1984, John Winchester suddenly finds himself with another little boy on his hands, one with dark, messy hair and sad blue eyes who won't leave John and his sons alone.
It's gen and has a really interesting Jimmy & Cas relationship as well as a family relationship w/ the Winchesters.
no subject
Summary: In 2009, Castiel watches the Apocalypse end disastrously and makes a decision. In 1984, John Winchester suddenly finds himself with another little boy on his hands, one with dark, messy hair and sad blue eyes who won't leave John and his sons alone.
It's gen and has a really interesting Jimmy & Cas relationship as well as a family relationship w/ the Winchesters.