Live Alone and Like It (a.k.a. An Unexpected Song) - S1-E19
Continuity mistake: Lynette opens the door while she has sunglasses on. Then she is holding her glasses. It never showed her taking off her sunglasses. (00:13:20)
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: 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.
Love Is in the Air (a.k.a. What I Did for Love) - S1-E14
Continuity mistake: When Bree Van De Kamp is sitting on the couch talking to her marriage counselor, as she is doing so she picks up her purse and puts it on her lap, crossing her hands over it. When the camera switches back to her a second later the purse is back on the couch beside her in the exact position it was in before she picked it up.
Continuity mistake: Caleb hits Melanie with a piece of lumber and she falls to the ground. She falls with her feet towards Caleb, but in the close up (and each scene after) her head is now towards Caleb.
Continuity mistake: Adam hands Katherine the note he found on the floor written by her aunt in a previous episode. Katherine is holding the paper up. When Adam walks around her in the next shot, the paper is gone and Katherine is only holding her keys/purse. The close up of Katherine (the very next shot) shows her holding the paper again.
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: 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)
It Wasn't Meant to Happen - S2-E20
Continuity mistake: While Susan and Edie are at the Hooters style restaurant, the amount of beer, and amount of head, in Edie's glass changes from shot to shot.
There's Something About a War - S2-E13
Continuity mistake: When Lynette and Tom are talking, Tom says "Really I got the job?" and puts down the newspaper he was just reading. In the next shot we see Lynette and you can see Tom is still holding the paper and puts it down again.
Like It Was - S3-E4
Continuity mistake: When Gabby and Carlos are driving in the car, Gabby's hair keeps switching from behind her ear when the shot changes.
If There's Anything I Can't Stand - S4-E4
Continuity mistake: The amount of cream on Victor's chest during his rubdown changes between shots.
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: 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: When Bree goes to see Zak, in one shot her hands are intercrossed, then in the next her arms are crossed. (00:17:55)
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.
There's Something About a War - S2-E13
Continuity mistake: As the nurse is talking to Susan about the operation, the folding of the paper the nurse is holding on the clipboard changes between shots. First it is half folded over, the next shot it has been folded right over and is being held right down. After this shot it changes again and is now folded back without her moving the paper.
It Wasn't Meant to Happen - S2-E20
Continuity mistake: When Gabrielle goes over to Dale to get him to sign the custody form for the baby; the sheet of paper is all creased and folded up. But when she shows it to Carlos it is not creased at all.
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.