Rotta is "stinky" enough without a diaper. It is assumed that he is wearng one. He has been in that cell on Teth for several days, and is very sick, so of course he has urinated, defecated, and vomited all over it. Noone has come in to clean or change the poor little Huttlet's diaper. This makes for a extremely malodorous situation.
Rotta isn't old enough to talk yet. so he is crying constantly. He is scared half to death. He is sick, crying, misses his Daddy, frightened, and in shock from being kidnapped and taken from his "family". He has lost weight, something Jabba notices immediately on his safe return by Ahsoka when Daddy picks up his son. It is inferred that he didn't eat or drink very much on Teth (there was noone to feed him. or make sure that he ate and drank.)
When his cell door opens, he starts screaming. I think that the Teth people poisoned him, to make sure that the Jedi had a very sick Huttlet on their hands. But they didn't want him to die, just to be in pain and obvious distress. so that the Jedi would want to rush him to a doctor They have to put him in some sort of container so that they can carry him, which of course he doesn't like and screams and struggles, creating great negative images for Count Dooku to show his father. . Fortuately for Rotta, he is an anomaly, a Hutt infant/toddler being raised outside his father/mother's brood pouch. So noone knows how much poison to give him. Hutts are extremely difficult to poison anyway (their robust digestive systems and super livers break down poison rapidly, and any damage done is quickly repaired through regeneration. Rotta is actually in little danger of dying, thanks toi his super Hutt constitunion. But noone knows this.
