Continuity mistake: You'll notice in some episodes (like "Coyote Piper") that when the sisters look out of the attic window, they can see Prescott Street below, indicating that the attic window is on the front of the house. But if you look at the size and shape of this window, you'll see that there is no window like this on the outside front of the house. In addition, in "Sin Francisco," Phoebe looks out the attic window and sees the front porch from a side view. There's no structure on that side of the house to begin with.
Continuity mistake: The furniture used throughout the show regularly gets blown up or destroyed but then mysteriously re appears later on or in the next episode.
Something Wicca This Way Comes - S1-E1
Continuity mistake: At the beginning of the episode they show Piper running up the stairs to her house in the rain. The umbrella she has is black, with a colored ring around the edge. When she enters the house the whole umbrella has changed to colors surrounding the whole umbrella now. (00:02:35)
Something Wicca This Way Comes - S1-E1
Continuity mistake: In the scene when Piper and Jeremy are in the taxi, Piper gives him a fortune cookie. You can see her closing the box. In the next shot of Jeremy, you can see the box is still open. (00:31:15)
Something Wicca This Way Comes - S1-E1
Continuity mistake: At the end of the episode the newspaper Prue is holding keeps changing from facing the camera to facing her. And as she turns to the house she drops her hand (and the newspaper) to her side but in the next shot she is holding it to her chest again. (00:40:25)
Something Wicca This Way Comes - S1-E1
Continuity mistake: At the beginning of the episode we see a man standing in the rain in front of the sisters house. After he starts walking away, they show a completely bare tree in front of the house. The next morning when Piper is driving away, they show the same tree with leaves and flowers on it. Trees do not grow that fast.
Something Wicca This Way Comes - S1-E1
Continuity mistake: When Piper and Jeremy are in the elevator, he pulls a knife on her she freezes him. When the camera shows him from her p.o.v he has this really "snarling" looking face with his mouth open. But when the camera changes the shot from looking at them from outside the elevator, his face is completely different and his mouth is almost closed.
I've Got You Under My Skin - S1-E2
Continuity mistake: When Phoebe flirts with Alec at Quake, she rests her head in her hand. In the following shots between Alec and Phoebe, her hand moves back and forth from her face to the tabletop. (00:02:00)
I've Got You Under My Skin - S1-E2
Continuity mistake: In the previous episode, Piper tried out for a job as a chef at a restaurant called "L'Opera Ristorante" and was hired by Chef Moore. Then in this episode, she works at a bar and restaurant called "Quake," but she talks about Chef Moore quitting and leaving her in charge of the establishment, so it's not meant to be a different place.
Thank You for Not Morphing - S1-E3
Continuity mistake: When Prue tells Victor to leave the auction house, Victor has his arms behind his back, but in the next shot, his arms are in front of him. (00:09:40)
Thank You for Not Morphing - S1-E3
Continuity mistake: In this episode one of the shape shifting demons from across the street attempted to take the book of shadows out of the house. He managed to carry the book to the door, but could not take it past the threshold of the house. But in the later series it is always stated that evil cannot touch the book of shadows.
Continuity mistake: When Prue runs into Susan Trudeau at the restaurant, she asks if she's Andy's sister, only to find she's his ex-wife. But Prue knew Andy all through high school - she would have known he didn't have a sister. (00:12:25)
The Truth Is Out There... and It Hurts - S1-E8
Continuity mistake: In the teaser, the demon attacks Dr. Mitchell, killing him and also destroying his irises. His eyes turn white, and later dialogue confirms that the irises were gone from his eyes. However, when the Charmed Ones find his corpse, his eyes are open and his irises are visible. (00:01:10)
The Truth Is Out There... and It Hurts - S1-E8
Continuity mistake: In this episode the truth spell is before the demons page in the Book of Shadows, but in 'Out of Sight' the truth spell is after the demons page.
Continuity mistake: When Prue describes the way the warlock Matthew traveled instantaneously, Melinda tells the sisters that it's called blinking, and that Matthew "must have copied it from another witch." But later in the series, every warlock encountered by the Charmed Ones had the ability to blink, and it was considered exclusively a warlock ability, meaning that no witch would have had it. (00:21:30)
Continuity mistake: When Prue lets Matthew out of the locket, the front view Prue has her right hand on her stomach, when the shot changes to the back view her hands are by her side, it does this multiple times.
Wicca Envy - S1-E10
Continuity mistake: At the beginning of the episode when Piper hides her sisters from Leo she has the shirt with the buttons closed, but between that scene the shirt is not closed. (00:01:05)
Wicca Envy - S1-E10
Continuity mistake: At the end of the episode, when Leo and Piper are saying goodbye he reaches out and touches her face, but when the angle changes his hands are instantly back at his side. (00:43:05)
The Wendigo - S1-E12
Continuity mistake: When Andy is lying on the ground unconscious The Wendigo rips open his shirt popping all the buttons, but in the closeup of Andy's face his shirt is still buttoned up. (00:38:50)
Continuity mistake: In this episode, Leo tells Phoebe that white lighters are sent to their charges by "a group of elder white lighters known as the founders." However, by later seasons in the series, the word "founders" was never used. The leaders of the white lighters were simply known as the "elders." (00:14:15)
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.