Every Day a Little Death - S1-E12
Continuity mistake: When Carlos pulls Gabrielle down to the sofa for a neck massage, he places the fried chicken bucket by his side on the sofa. When Gabrielle stands up and refuses to have a baby, the bucket has disappeared, and when we see Carlos leaning back on the sofa a few moments later, he has the bucket held in his arm.
Every Day a Little Death - S1-E12
Continuity mistake: When Edie gets the phone call, saying Mrs Huber was found, while she is at Mike's, you can see the cell phone on the table where she is sitting. When the phone rings, she reaches to nowhere with her right hand and you can still see the phone. Then the view changes and you can see her getting the call with her left hand.
You Could Drive a Person Crazy - S2-E2
Continuity mistake: When Susan is screaming at Edie and she's going away, Susan's hands change position between shots.
Continuity mistake: Lynette goes to her second interview and has to take her daughter with her. When she is talking to Stu the receptionist he is eating a long sandwich. In the initial shots the sandwich is whole, but by the final cut away the sandwich has been cut in half lengthways, with the second half now on the desk in front of him.
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.
Like It Was - S3-E4
Continuity mistake: When we see a close up of Orson making a cup of Cappuccino, you can see the cup is filled with steamed-milk foam, but as the scene changes there is less foam in the cup than there was in the previous shot.
Mother Said - S4-E15
Continuity mistake: When Tom tells Lynette that Kayla is frightened of her because she hit her, the bedroom door behind him closes slightly between shots.
Visible crew/equipment: When Carlos is speaking to Charles (Travers' father) outside about joint custody and Charles says "Y'know, I just don't get it", a boom mic and pole are reflected in one of the windows near the front door of the house.
Visible crew/equipment: When Ed opens his car door for Lynette, the camera crew are reflected in the side of his car.
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.
Continuity mistake: After Gabby throws John out of the hotel room, she locks the door. But when Carlos leaves the room, he opens the door without having to unlock it.
Audio problem: When Gaby sees Paulina Poriskova in the restaurant, she puts out her arms and says, "Give me a hug!" but her lips barely move.
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.