Plot hole: When Zach Young's grandfather died, Zach was said to be the sole heir of the fortune. However, Noah Taylor (the grandfather) had a daughter that appeared several times while Mike Delfino was looking for Deirdre. Where was Kendra Taylor while Zachary Young was spending Noah's fortune on dresses for Gabrielle Solis? Why didn't she claim her share? She simply disappeared.
Other mistake: In season 3 it's revealed that Mike Delfino's doctor at the hospital is Ida Greenberg's nephew. When Ida dies in season 4 her only distant relatives come from another state, and there's no trace of her nephew from Fairview.
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.
Plot hole: It says on Mary-Alice's tomb stone that she died on September 26th 2004, which was a Sunday, yet in the first episode, she says that she died on a Thursday.
Deliberate mistake: In the episode where Mary-Alice Young's house is open for buyer's inspection, the phone number on the "For Sale" sign has been digitally blurred.
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.
Factual error: In the ep in season four where Victor drifts ashore, someone calls the police officer at Gabrielle's home and informs him that Victor has been found. The officer answers the call, listens for about one second and then hangs up. In that one second he's gotten four sentences of information to pass on to Gabrielle about her husbands whereabouts. There wouldn't have been time to tell him so much in so little time.
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.
Factual error: When Gabrielle becomes a widow she marries Carlos again in front of a priest. But the Catholic Church doesn't admit divorce, so in their eyes Gabrielle and Carlos were still married. They should have repeated a civil wedding, since only the civil effects of marriage were ended with their divorce.
Audio problem: When Gaby's charity modelling event takes place and Susan, after being roughed up by John Rolland's mother after mistakenly accusing her of sleeping with her son, Tom starts talking but you can see him in the left corner of the scene without his mouth moving at all.
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.
Visible crew/equipment: In one of the episodes, Gabby has her Maserati car taken from her by the repo guy. When he pulls off, the car is towed behind him. Clearly reflected in the metallic paint of the Maserati is the crew, with boom, camera and everything else.
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)
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.