Plot hole: Several days must have passed between the teaser of this episode and the rest of it, since Gabrielle has had time to make up (very professional-looking) cards and posters, gotten several dozen volunteers and reserved dresses for many of them, yet Paul has only just gotten around to disposing of Mrs. Huber's body and trying to wash the blood out of his shirt. Even if we assume the teaser takes place right after the end of the last episode (when Paul murdered her), that's still several days of keeping a rotting corpse and enough evidence to put him away for life around his house.
Continuity mistake: When Bree gets out of the golf cart to see Rex on the field, she is carrying a pot of urine in her left hand, but in the next shot, of her upper torso and face, her left hand is clutching the strap of her handbag and the pot is now in her right hand.
Continuity mistake: When Lynette is sitting on the bench chatting to Claire in the park, you can see that Lynette has her hand on the pram, but when the camera angle is behind Lynette in other shots, she no longer does.
Continuity mistake: When Lynette sits down next to Claire on the bench at the park, Claire is wiping her hands with a tissue. Claire is not wiping her hands in the next shot, but in the shot after that, she is.
Continuity mistake: When Lynette introduces herself to Claire at the park, the strap on her handbag is on her shoulder. When the camera angle changes to behind Lynette in the next shot, the strap has gone, and in the shot after that, it is back again.
Audio problem: When the Stagehand says "Come on, you're up!" to Susan before she is about to go on the catwalk at Gabrielle's fashion show, the words do not match his lips.
Continuity mistake: When Zach is in Julie's bedroom, he says to her, "And they buried her, to protect me" and you can see that Zach has his hand on his cheek. When the camera angle changes to behind Zach in the next shot, he no longer does.
Continuity mistake: Before the fight between Helen and Susan at the fashion show, Susan has a flower in her hair. There is no sign of the flower when Helen tears off part of her wedding dress, but when Susan says "What?", the flower is back again.
Audio problem: When Susan is on the catwalk at Gabrielle's fashion show, Tom announces what she is wearing, but if you look in the background you can see his lips are not moving when he is speaking.
Continuity mistake: When John is speaking to Susan about his relationship with Gabrielle, Susan puts her hand on John's cheek, but in the next shot, when John's mother is looking out of her car, Susan can be seen with her hand on John's shoulder.
Continuity mistake: In the scene where Bree and Lynette are talking about nannies, Lynette is in the back seat strapping her baby daughter into the car seat. In the shot facing Bree, Lynette takes a baby toy lying on the back seat and hands it to her daughter, but in the next shot facing Bree, the toy is back on top of the seat where again Lynette hands it to her baby.
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.