The Middle Season 2 Episode 3 (The Middle s02e03) with title “The Diaper Incident” aired on Wednesday, October 6th 2010 at 08:00 pm via ABC Network.
Here is summary for The Middle Season 2 Episode 3 :

Frankie is humiliated when she goes shopping for baby diapers for Sue, who has run out of them while babysitting, and the clerk thinks she’s looking for adult diapers. Elsewhere, Frankie makes Mike take a physical, thinking he’s starting to break down