Character mistake: In the attic, Melinda Warren is awed at how thick the Book of Shadows has gotten. But according to information from previous episodes, the Book was started after Melinda had died, so she wouldn't know how thick or not it was.
Charmed (1998)
1 character mistake in season 1 - chronological order
The Importance of Being Phoebe - S5-E11
Continuity mistake: When Phoebe is lying on the ground and is supposed to be unconscious, when Cole goes to pick her up you can see Phoebe throw her arms around his neck. (00:29:15)
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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.