Plot hole: Throughout the series, it's established that good witches don't freeze. In this episode, however, Little Piper freezes Future Prue and Piper when they come back to the manor to "kidnap" their younger selves. Simply because the Charmed Ones reason that only one "set" of sisters (past/future) could have their powers doesn't mean that Future Prue, Piper and Phoebe aren't good witches. In other time-travel episodes, the sisters remain immune to freezing and are still able to say spells make potions, meaning they are still good witches. For example, in Season 8 "Forever Charmed," Piper and Leo go back to 1975 (the same time-period as this episode) using Coop's ring, trying to find when Phoebe is alive again. However, when a startled Patty tries to freeze them, only Leo freezes. Piper does not, though she likely cannot use her freezing/exploding power in this time.

Charmed (1998)
1 plot hole in That '70s Episode - 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)
Cole: Phoebe, I love you. I don't know what's going on but maybe I can help. Would you like me to kill someone for you?
Trivia: Many actors who have made appearances on Charmed have also made appearances in Buffy. Some are Greg Vaughn, Charlie Weber, Wade Andrew Williams, Kevin Weisman, Christopher Wiehl, Daniel Dae Kim, Michael Bailey Smith and Brian Thompson and Charisma Carpenter.
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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.