Audio problem: When Eva Longorea drives home her husband is talking to a man. Their lips move, but no sound comes out.
Continuity mistake: When Gabrielle and Carlos go out of the house to investigate what is happening when the Chinese maid starts shouting, they close the door behind them. In the following shots the door is open again.
Continuity mistake: While Betty Applewhite is talking to Bree about her son Caleb, the amount of wine in Bree's glass changes constantly throughout the scene without her ever touching the glass.
Visible crew/equipment: As Susan and Edie approach Bree to ask her about the Applewhites, a camera crew is reflected in the side of Bree's car.
Answer: Kayla was sent away in episode 16 (The Gun Song) in season 4, after falsely accusing Lynette of child abuse. She now lives with her grandparents - probably Nora's parents.
I'm curious why we never see her again, why she never talked about, and why Tom never mentions visiting her.