Visible crew/equipment: Just after Paige casts the spell to rid Piper and Leo of the gods inside them, the tip of the boom mike is just in shot above Paige's head. (00:33:10)
Sleuthing With the Enemy - S3-E8
Revealing mistake: When Phoebe throws the potion at Cole's coat, the vial doesn't shatter, even though it sounds like it. Watch closely, and you'll see the purple, unbroken vial bounce off the coat and away out of shot without any of the potion touching the coat.
Revealing mistake: When the sisters are talking in the kitchen about Phoebe crashing Prue's car, whenever Phoebe turns around you can see a distinctly grey patch of skin on her shoulder where one of the actress's tattoos is covered up.
Witchstock - S6-E11
Continuity mistake: Robin falls over backwards after Paige dumps a cannister of marbles onto the floor. But Robin wasn't moving at all when this happened. Trying to walk over marbles will make you fall. Standing still while marbles roll around and bounce off your feet? Not so much.
Continuity mistake: When Prue talks to Piper after stopping her phone conversation, she tells her that "the Sin Balls work a lot faster than [they] thought. Once infected, the victim only has a few hours before it drives them to total self-destruction." However, this is almost verbatim what was written in the Book of Shadows. It could be easily read by the viewing audience when the book entry was shown. So all three sisters should already know this.
Charrrmed! - S7-E4
Revealing mistake: When Leo is on top of the bridge meditating; the water shown in the background is not moving. Also, cars on the bridge move, but often change speeds rather dramatically (sometimes moving fast and other times moving incredibly slowly).
Continuity mistake: When Kate was drawing the trolls in one shot she had a peach coloured crayon, and in the next shot she had a purple crayon.
Plot hole: When Prue first releases Matthew, he blinks several times, then blows out the windows and jumps out. Why would he do this and reveal who and what he is when he could have simply blinked? Obviously it was just a way to get the police involved so Andy could be chasing Prue through the episode.
Continuity mistake: In this episode, Chris thinks back to when he went back to the past. When he and Bianca are on the tour of the manor, there are some costumes that have been worn by the charmed ones. But in the episode "Oh My Goddess (1)" Chris tells Phoebe that Paige died on that day, so how could she have worn something after she died? And if she did die that day, Chris would have never met her, since he was not yet born, and could not have learned to orb from her, as he says in "Spin City." However there are other inconsistencies with that story that Chris mentions later, seeming to suggest he lied about this to get the sisters onside. It may not be a continuity error but as it was never fully addressed in the show just what Chris was lying about (and he obviously told some) we cannot be sure.
Revealing mistake: When Paige cuts the flesh away from Sykes, you can visibly see a white bandage-like thing under his skin as it comes off. (00:23:20)
Revealing mistake: In the beginning of the episode, Yenlo and Anling are fighting with swords. After Yenlo says, "I'm going to kill him, Anling. And then I'm going to kill you," Anling stabs him with her sword. Yenlos' wound is very bloody, but there is no blood on Anling's sword at all. (00:04:25)
Desperate Housewitches - S8-E4
Continuity mistake: Paige asks how The Source was previously vanquished, but she was there both times: when the original Source was vanquished, and again when they vanquished Cole. Also Phoebe wasn't actually there for the final vanquish of Cole, but was taken back by Cupid as if it was her memory.
Charmed and Dangerous - S4-E13
Revealing mistake: During the episode, Paige is wearing a sleeveless top, but when she thrown across the attic by 'The Source' the stunt double is wearing sleeves. (00:37:45)
Be Careful What You Witch For - S2-E22
Continuity mistake: When Phoebe and Piper are leaving to go get Prue, Piper kisses Leo on the cheek and there is a lipstick mark on his cheek. Then the shot goes to Piper then back to Leo, and the mark has gone with no time for him to remove it.
Coyote Piper - S3-E9
Revealing mistake: Prue knocked Piper unconscious in the cat fight (after the Coyote Dance), and asked Justin to carry her to the car. But when he is apparently lifting Piper up from the floor, you see Piper standing up by herself.
Chick Flick - S2-E18
Continuity mistake: In the teaser, Phoebe took off her messenger bag while she was sitting in the chair talking to Prue, and she left it there when she went up to get the door. For the rest of the scene at the house, including when Phoebe and Prue ran out of the door, Phoebe was not wearing the bag. Then, when we saw them outside immediately thereafter, Phoebe was wearing the bag again.
Visible crew/equipment: When Paige explains to Phoebe that someone tried to kidnap baby Chris, when the shot is on Paige you can see the white tape of the actor's cue marks on the floor. (00:29:05)
The Legend of Sleepy Halliwell - S6-E14
Other mistake: When Phoebe arrives back from her vision quest to find Piper has been kidnapped she tries to sense from the frozen students which one created the headless horseman. As Gideon, Paige, Chris and Phoebe walk into the conservatory you see Zachery blink rather obviously.
Revealing mistake: At the end when Prue is fighting the demon you can tell she is holding on to her safety harness when she is in the air kicking him.
Siren Song - S5-E4
Revealing mistake: When the Siren is being healed, you can see that she's just holding the pole next to her, when it's supposed to be going straight through her. (00:19:50)
Answer: That was a mistake in the series.
Also, the episode is called 'Babies First Demon' and this alone tells us that it's Wyatt's first time in the field (so to speak) and as the sisters say, they've done a good job of clearing up their own magical messes so far. Nobody really knows how advanced Wyatt's powers are, or will become. That's why the cleaners appear, to nip things in the bud. The Cleaners didn't want to chance that the sisters could clean Wyatt's magic up, just incase they couldn't. Therefore intervening themselves, just in case.