The Kids Are All Fight

"The Kids Are All Fight" is a Season 26 episode. On November 11, Al Jean wrote on twitter that this would be a Bart and Lisa flashback episode. It takes place when Lisa was two years old and Bart was four years old. It aired on April 26, 2015.

Synopsis
When Homer gets an old film roll developed, the family takes a trip down memory lane to see the origins of how Bart and Lisa first started getting along with each other.