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.
Factual error: Considering how the sisters and Cole every now and then - especially during seasons 3-5 - find themselves in some churchyard or cemetery, it should be noted that there are no such places in San Francisco! Except for the original one at an old nunnery, from before the city was founded, and the Presidio Military Churchyard, all graves were moved in the first half of the 20th Century to the cemeteries at Colma, a few miles south of SF. This was done due to the sanitary risks in case of earthquakes, and the lack of space for churchyards downtown.
Revealing mistake: Throughout the series, Finola Hughes appeared as Patty, the deceased mother of the Charmed Ones. Although Patty died in 1978, she sometimes appeared in flashbacks and time-travel episodes that took place in the mid to late 1970s, and other times she appeared as a ghost. However, over the eight years of the series, Finola Hughes aged noticeably. Patty was born in 1950, so she should always have been either a young woman in her mid 20s, or an unaging ghost having died at 28.
Factual error: Throughout season 8 the members of the Triad wore a pentagrams on their gowns that would alternate from the point being up and point being down. They should only be wearing a pentagram with the point facing down. Pentagrams with the point facing up is the symbol for practitioners of white (good) magic while those who practice black (evil) magic is symbolized by the point facing down.
Factual error: Numerous times in the establishing shots of San Francisco, the Embarcadero Freeway is visible. While the bridge did run along the San Francisco Bay, it was demolished in 1991 - seven years before the series even started.
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.
Other mistake: Prue tells Andy about her powers and he asks her if when she has kids they would inherit them - she says "If they are girls, yes" but later on in the series Piper has two boys who are both very powerful. (00:30:30)
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.