Plot hole: When Paige and Leo are talking in Leo's office at magic school, Paige compliments Leo for being such a good headmaster. She mentions that after being headmistress for a year, it's harder than it looks. If she became headmistress after they killed Gideon (i.e. when baby Chris is born) and she's been headmistress for a year, that would make Chris at least a year old. Chris is obviously not one year old just yet.
Other mistake: In both scenes in which Phoebe's hair is cut, her hair is up, with very little loose hair. There is no way that the amount of hair shown to be cut in both scenes could have come from her head. In the first scene, it is very clear when the demon cuts her hair, it is a few tendrils, yet when he is shown with Imara, it is a very measurable amount of hair. The super speedy guy who cut her hair the 2nd time, when she was Imara, was too quick to see the actual amount cut, but again, because of her hairstyle, he could not have cut the amount he shows to the Charmed Ones in the next scene.