Visible crew/equipment: In the beginning when Niles lets C.C. in the house and she puts an envelope on the table, you can see a crew member start to step out through the hall in the background and step back real quick. Then as C.C. starts to walk back to the door, you can see them step back out to cross over.
Continuity mistake: The smash vase is placed on the office desk by Niles, it keeps jumping back and forth between two different orientations between scenes. (00:10:34 - 00:12:57)
Revealing mistake: Ms Babcock enters the house and stands by the small table You can see Maggie in the hallway behind her come out for her scene too early and duck back out of sight, and then quickly re-enter the scene just as the camera pans away. (00:07:20)
Answer: Mr. Sheffield needed someone to manage the kids, not necessarily babysit them. Brighton was a Bart Simpson type, Maggie was shy and awkward and Gracie had personality issues.