Continuity mistake: During the dinner scene at the Van der Kamp's home, Danielle throws her plate against a wall, but when they pan back to her, the plate is still on the dinner table.
Continuity mistake: When Julie is tutoring Austin, he takes out a beer can, drinks it, crushes it and puts it down on the desk. A couple of shots later when Julie stands up, the beer can has rotated itself slightly without Austin touching it.
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.