Continuity mistake: When Phoebe is walking the Dwarf to the door after finding out Piper pulled the sword from the stone, he steps outside and goes into fast-forward, then stops and goes back to normal speed as he sniffs a flower. During this, in the background, you can see Phoebe, who freezes the whole time. (00:18:40)
Continuity mistake: As Piper is talking to Mordaunt at the Round Table, her fringe changes from in front of her face to behind her ear to in front of her face again.
Continuity mistake: When the sisters first see the lady in the lake, the demon off to the side throws a knife into her back, but the knife hits completely straight, as it would if the demon had been directly behind her.
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.