Be Careful What You Witch For - S2-E22
Visible crew/equipment: While Leo is up in the attic with Piper, flying Phoebe, and teenage Prue, Leo explains what happened to Prue, and when Phoebe asks how it's even possible, we can see the stunt harness at the back of Phoebe's jeans as she rises in the air. (00:18:45)
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.