Dean and Sam find a little boy who is traumatised/too young to talk/know his name. Dean keeps swearing they'll drop him off at the next 'safe-haven/CPS' place they come across. They end up hanging on to him. Both Dean and Sam teach him to use the 'puppy!eyes' against the other. At one point he calls Sam 'Smammy' and a clerk thinks he said mommy and awwww'ed over it, Sam of course huffed unhappily.

ETA: Found! Link in Comments