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.
Continuity mistake: Phoebe had to touch both Jane and Malcolm for them to be trapped in the painting, so how come she didn't have to touch Piper and Prue for them to all be freed? (00:39:25)
Continuity mistake: When Piper writes the name "Nell" backwards on the castle window she uses two fingers so each letter is doubled lined, but when the name is viewed from the outside all the letters are single lined. Additionally, after she writes the backwards "N" on the bottom right window, in the next closeup of the swords' pointy ends that window is blank. (00:30:20)
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.