B & E are just starting to "play" with each other. This may entail B being B and making E laugh in the process, holding hands, B making E roll over (he says, "Mama, I make Baby Sister roll like a ball!" - yeah, this requires a little adult supervision), B sharing his "bayntdee" (blanket) with E and so on. Too much fun!
(There were way too many cute pictures from this bunch...I couldn't pick just one!)