Continuity mistake: In season 1 it's revealed that Lynette and Tom first met when working for the same company, and Tom left his girlfriend for Lynette. In season 7 it's stated that they were already dating in college, and Tom betrayed Lynette with her friend Renee.
Continuity mistake: Series 3 Episode 1: When Bree welcomes Carolyn to the engagement party, she is holding a tray in her hands, but when Carolyn starts telling her about Orson's past, the tray is gone.
Continuity mistake: On the note Mary Alice receives that leads to her suicide, the position of the three sentences changes throughout the series. In episode 1.1 (Pilot), all three lines are written on the top half of the note (above the crease), but in later episodes the first two lines are on the top and the third is on the lower half. The left margin also gets smaller, and the handwriting varies slightly.
Continuity mistake: When Betty is shown the crime scene photo of Melanie's body, Melanie is inches away from a pallet and the jacket covers most of her torso leaving only the right arm exposed. In the flashback scene, Melanie is feet away from the pallet and the jacket mainly covers her chest and face, leaving both arms uncovered.
Continuity mistake: In episode "The Gun Song, Free Part 2," when Gabby runs upstairs to confront Ellie, her headband is further on her head than when she runs into the bedroom.
Continuity mistake: Throughout the series, any time you see into the front door of the Scavo house (from an exterior shot), there is a blue wall with a table in front of it, however, interior shots show that the front door leads to the lounge, with the staircase opposite the door.
Continuity mistake: Season 3, Episode 6: "Sweetheart, I Have to Confess" - When Gabrielle suggests that her and Carlos don't go through with their divorce, her head is resting on Carlos' chest. But in the next shot, it isn't.
Continuity mistake: When Bree Van De Kamp is first shown with her muffins, we see that the hand towel on the right basket is not in her hand, then when the shot changes it is. (00:05:20)
Continuity mistake: When Lynette comes out of the pool, after getting her boys, she is wearing high heels, but when the shot changes to a distance, she isn't wearing anything on her feet. (00:13:15)
Continuity mistake: Season 1, episode 1 (Pilot): While Gaby and Carlos are arguing in their house, we can see a sofa and some other items in a semi-circular alcove with five tall windows on the far wall of the front room, and a painting near the stairs. A minute later, Carlos leaves and Gaby is alone with John, and the room has changed drastically. The alcove is now a flat wall with two windows and a fireplace. The sofa and some other things are missing and the painting moved to above the fireplace. This inconsistency exists because after the pilot was filmed, the set was redesigned and the part of John Rowland was recast. The scenes with John were reshot after the redesign took place, but the majority of this episode, including the first half of this scene (the argument), used the original footage. (00:17:30)
Continuity mistake: When Rex Van De Kamp is at the restaurant, his fork is half way over his napkin then in a later shot it's completely on the napkin. (00:26:50)
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)
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.
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)
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.