Continuity mistake: Susan's house is burned down by Edie towards the end of season 2, but at the beginning of season 3 the house is exactly as is back to normal and as it was before the fire.
It Takes Two - S3-E2
Continuity mistake: While preparing for Bree's wedding, Susan is seen wearing full hair curlers for the entire day, yet on the day of the wedding, her hair is straight without a single curl.
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.
Like It Was - S3-E4
Continuity mistake: When Bree is talking to Vera about Andrew and her husband, Vera is holding a nearly empty glass of tea. She then fills the glass to the top, but when she picks up the glass after doing so, it's nearly empty again.
Like It Was - S3-E4
Continuity mistake: When Bree goes round to visit Vera, the camera is reflected in the door as Vera opens it.
Like It Was - S3-E4
Continuity mistake: When we see a close up of Orson making a cup of Cappuccino, you can see the cup is filled with steamed-milk foam, but as the scene changes there is less foam in the cup than there was in the previous shot.
Continuity mistake: During the dinner scene at the Van der Kamp's home, Danielle throws her plate against a wall, but when they pan back to her, the plate is still on the dinner table.
Continuity mistake: When Julie is tutoring Austin, he takes out a beer can, drinks it, crushes it and puts it down on the desk. A couple of shots later when Julie stands up, the beer can has rotated itself slightly without Austin touching it.
Sweetheart, I Have to Confess - S3-E6
Continuity mistake: During the scene with Tom and Nora in the pizza parlour, a wine bottle and a glass are knocked over in an argument. When they pan back to the table as Nora is leaving, the full bottle and the glass are back on the table.
Continuity mistake: When Nora dies, Lynette stands up and strokes her hand over her chin, so a little blood stays on her chin. During the yelling scene of Lynette towards Carolyn, the blood on her chin changes constantly between shots.
Continuity mistake: In the scene where Carolyn shoots Lynette, Lynette is wearing high heels when she is originally shot. But when Lynette falls into Art's arms, she is wearing shoes without heels.
Continuity mistake: When Gabrielle is at Bill's home drinking a glass of wine, the amount of wine in her glass changes several times as the camera changes position, without Gabrielle drinking any of it.
Continuity mistake: When Bree throws a glass of water of Orson to wake him up, the upper part of his shirt goes from being spotted with water to being soaked.
Continuity mistake: When Tom is proposing a toast to Lynette in the bar, he's holding the coffee with his left hand. However, in the next shot he's drinking the coffee with his right hand, and when the shot changes he's holding the coffee in his left again.
Continuity mistake: During the dinner scene, Ian starts to pour his mother some wine, but in the very next shot, he starts to pour it again.
Continuity mistake: Carlos swiped every thing from the table but a fork appears behind Edie. (00:18:35)
Continuity mistake: When Lynette sends Kayla upstairs, her bag is seen both on her shoulder and in her hand between shots.
Continuity mistake: When the boy paints "witch" on Mrs. McCluskey's front door, he holds the container in his left hand and the brush in his right. But when Karen gets out and he runs away with the other kids, the two items switch positions.
Getting Married Today - S3-E23
Continuity mistake: Gabby's hair in the beginning has her bun high on her head and her tiara is visible from the front. When Bree walks in, and when she overhears Victor and his father talking, her tiara is farther back on her head and no longer visible from the front.
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.