One of these things just doesn't belong . . .

We had haircuts today. Porter went first - his first haircut ever - and did pretty well, all things considered. Lincoln joined Porter shortly thereafter, when his haircut was complete. I got Porter out of the tub and dressed before Ethan got in. I then proceeded to clean up the hairy mess in the kitchen. A few minutes later - over the noise of the vacuum - I heard screeches of delight. I made my way to the bathroom where I found this:

Can you find the boy who doesn't belong?