You'll Never Get Away From Me - S2-E3
Visible crew/equipment: When Phyllis leaves in the taxi, a boom mic is reflected in the taxi's rear window.
Color and Light (a.k.a. I Must Be Dreaming) - S2-E7
Visible crew/equipment: Right at the beginning of the episode, we see a woman drop her daughter off at a strangers house. When the front door opens, a camera crew is reflected in the brass door knocker.
It Wasn't Meant to Happen - S2-E20
Visible crew/equipment: When Edie discovers that Karl is leaving her for someone else and drops the letter that he wrote for her, a boom mic is reflected in the windscreen of her car.
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.