Dean and Sam did end up like Livia/Eve kinda

Dean and Sam did end up like Livia/Eve kinda

So basically SPN season 12 is like all those media where due to Reasons the hero's baby is instantly grown-up so the hero and the baby can interact as peers*, except instead of it being done from the hero's POV (where they and the viewer are disconcerted that the baby is suddenly their own person), we're seeing the story from the baby's POV (where they and the viewer have all the context that the parent doesn't).

*Xena's Eve, Angel's Connor, Charmed's Chris Halliwell, Once Upon a Time's Rumple & Belle baby