"The big sister sits on the couch smugly."
There she can be the one getting yelled at, enter. You look up confused she hadn't changed but everything looks bigger now.
"See diaper butt? Daddy says I don't have to play with you right now."
What diaper butt? You look down and it all makes sense. Mary is the big sister because you're younger now. No more than 2 years old and dressed in only a diaper. This isn't what you wanted. Time for another change, or it would be if Mary didn't grab the phone from your hands.
"Hey where'd you get this?"
"Dat's mine, Mary!"
"No, little babies like you don't get phones I don't even have a phone. Now let's see what you were messing with."