Continuity mistake: When Lynette is feeding her baby, we see from behind there is a backpack on her chair then when the shot changes it is not there. (00:29:55)
Visible crew/equipment: Just before the fire starts you can see a crew member's legs/feet on the right side of the couch. (00:38:06)
Visible crew/equipment: When Susan sits on the couch in Edie's house, just after she throws the bra behind her and knocks the candles over, a crew member in blue jeans can be seen moving on the floor behind the couch to the right.
Continuity mistake: During the scene where Gaby and John are in her bedroom talking, she takes a drag from her cigarette while John asks why she isn't happy, but never exhales the smoke from that drag. 23 seconds pass from that drag to the next one and she's in frame the entire time (it cuts between shots of the two of them together and Gaby's close-ups, but doesn't cut away from her). It's also worth noting that Gaby is never seen smoking again at any other point in the series and no explanation is given as to why.
Continuity mistake: When Lynette is in the supermarket, right after she loses track of the twins, she is seen pushing her shopping cart down the aisle,and in the seat there's only a pink blanket. But when she sees Nelly Klein, her baby daughter is sitting in the seat with the blanket and one of her sons is riding in the basket.
Continuity mistake: In the restaurant, Bree makes a salad for Rex at the salad bar. It is fairly tall with lots of tomatoes. The salad she gives him is flatter and missing many of the tomatoes.
Visible crew/equipment: When Bree is watering the flowers in the bathroom at the hospital, a shadow of the cameraman is visible behind her.
Continuity mistake: When we see Lynette driving her kids, in the first shot we see some red, blue and white decoration in the front of the car to the right, then when the shot changes it's in the centre. (00:13:50)
Continuity mistake: When Mike comes home with the shopping bag, we see that the items in his shopping bag change positions in between the shots when he goes to see Edie arrive. (00:20:30)
Continuity mistake: When Mike is taking his dog to the vet, we see that Susan's hair is covering her ear in all the shots except the last one when her hair is behind her ear to show that the earring is gone. (00:39:30)
Continuity mistake: When Julie is leaving we see that she leaves the door open and then it closes with a slight open gap, yet just for one shot the door is completely closed, then it's open again. (00:09:50)
Continuity mistake: When Lynette gives her husband his photo, the position of the photo changes in between shots. (00:13:05)
Continuity mistake: When Gabrielle and Carlos are saying hello to Ashley, the position of her hands change on the ball, from the front to the side to the front again. (00:14:40)
Continuity mistake: When Karl is speaking to Susan whilst she's in the towel, we see in one shot his chin is resting on his palm, then when the shot changes he tilts his head and then moves his fingers to his chin then when the shot changes his chin is resting on his palm again. (00:25:00)
Continuity mistake: When Bree steals Mary Alice's tape in Dr Goldstein's room, she takes it with her right hand and grabs it to her waist while she raises her left hand to her hair. In the next shot when the doctor enters the room, you can see her right hand is up, and when the camera comes on her the next shot, her left hand is up again.
Revealing mistake: In the episode where Teri Hatcher's character is in the supermarket, as you see her place her two items, a carton of OJ and a carton of eggs, listen closely. The items are empty -- quite obviously so. (00:17:45)
Continuity mistake: When Susan and Mrs.Huber are together in the Supermarket the position of the egg box keeps changing in between shots on the conveyor belt. (00:18:00)
Continuity mistake: When Lynette and Gabrielle are talking to Paul, the boxes Gabrielle are holding change position between shots under her arms. (00:34:30)
Continuity mistake: When Andrew is talking to his mum, Bree, on his bed, we see him put the magazine down, yet in a later shot it is no longer there. (00:38:10)
Continuity mistake: When Lynette is at the school, the teacher is waiting outside eating. If you look at her hands, you can see that she has a white napkin. The napkin changes from one hand to the other between shots, and in one shot it is small and the other it is not.
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.