Kenny is a short boy, about the same height as Maureen. He has dark, mustard-blonde hair that covers his eyebrows, making it hard to tell what emotion he's expressing. He has what is either buck teeth or a mild overbite, as teeth always portrude from his mouth whether it's closed or not. Clothing-wise, he is always seen wearing a purple t-shirt with black stripes on the sleeves which is too small for him, exposing his belly, a green baseball cap, a pair of pulled-up socks with sandals on, and most notably, a large diaper which seems to constantly sag. When climate began getting colder, he adapted a small green scarf. He was also briefly seen donning a "pink pillow" which was stuffed into his shirt and diaper, which turned out to be fiberglass insulation.
Worth noting is his bizarre posture, as his waist is thin and his back is arched slightly, making is rear stick out, while almost always standing bowlegged and sitting with his legs apart, this could be due to the show's art style, or possibly the diaper he wears being full.
Much like his brother, though to a more extreme extent, he is incredibly stupid, constantly pressuring Maureen and Bill into doing stupid things alongside his brother, Ben. Despite this, he's less an antagonist and more of a nuisance, as only Bill seems to have any issue with him. He gets along well with Maureen. He also seems to lack the concept of personal space, as he actively offers Bill fiberglass he had in his diaper, and let himself into the Murphy household while no one was home, sitting down to watch their television. He'd later tell Frank about the latest Colt Luger special, to which Frank thanked him, showing no disdain for his unauthorized entrance into their home (Frank didn't even reprimand him, as he was too fazed by Bill's forest fire and because Kenny had seen the entire Colt Luger episode). This would happen again in Season 3, where Kenny spoke to Frank on the doorstep and asked if he could eat a fire cracker. Frank politely iunformed him that it wasn't food and lit it to demonstrate. Kenny simply held the lit firework as Frank walked away, causing it to blow up in his hand.
Not much is known about his and Ben's family or if they even have any. They both seem to be under some sort of care, as they both seem fairly healthy. Kenny once mentioned that Bill's magnet tastes like "Mama's gun", which proves they at least have a mother. However, after getting fed up with the cold weather, Kenny remarked he was going home, before crawling into an empty washing machine/dryer.