Other mistake: When Sylvia is outside the Sheffield mansion she says "I wonder if my daughter Fran is at home? I will see if she is" the doorbell rings as soon as she finishes that line, but you can see both her hands are visible. She can't have rung the doorbell.
Continuity mistake: When Fran's date Jack first enters the house, Fran closes the door behind him. A couple of shots later, the door is open and Fran is closing it again.
Franny and the Professor - S3-E2
Continuity mistake: At the end of this episode Fran is on the phone with the people from Jeopardy saying she only got 5 boxes of the rice-a-roni but when they show her again talking to Maxwell, Fran now has 6 boxes of rice-a-roni.
Continuity mistake: When CC and Maxwell are hiding in CC's closet, the coat CC is hiding behind changes between shots. Some shots she is hiding behind Charles Haste's grey coat and other shots Fran's gold one.
Other mistake: In some episodes, there is a small room between the kitchen and dining room (the "Butler's Pantry"), but in other episodes the same door leads directly into the dining room, and in still others it leads into a passage.
Revealing mistake: When Fran is on the private jet, the champagne sitting between her and Cathy doesn't move through all the turbulence, showing that it is the camera shaking and not the plane.
Revealing mistake: As Chloe Simpson is leaving the mansion at the end of the show, she trips over Fran's foot without touching her. She starts to trip about half a foot before Fran's shoe.
Continuity mistake: None of the Sheffield children are aged properly over the course of the series. It's established that Grace is 6 years old in season 1, but two years later in season 3 she's 10. Maggie is 18 at the end of season 5 but turns 21 years old in early season 6. And finally, Brighton is in seventh grade in season 2 and somehow is graduating high school at the end of season 6 (when he should be only a junior, and nothing about Brighton's character would suggest he's capable of skipping a grade).
Continuity mistake: In the kitchen, while Fran is telling Maxwell about Brighton and Tiffany in the shower, the glass of juice on the counter appears and disappears between shots.
Continuity mistake: In the opening titles sequence, cartoon Fran is thrown out of the bridal shop and the doors are closed behind her. When she hails a taxi in the next shot the doors are open again.
The Nuchslep - S1-E4
Continuity mistake: When the Chinese food is delivered, Fran's hair is very flat and the curls are loose. In the next scene, she goes to talk to Maxwell and her hair is noticeably curlier.
Continuity mistake: When Maxwell is talking to Brighton about the battle of the sexes, he puts his hands in his pockets. The shot changes and suddenly his hands are at his sides and he puts them in his pockets again.
The Butler, the Husband, the Wife and Her Mother - S1-E6
Continuity mistake: When Sylivia is telling Fran about her birth, she raises her right hand and has her left hand on her hip. When the shot changes her left hand is raised and her right hand is on her hip.
Continuity mistake: In the opening sequence, Fran arrives at the Scheffield house with a case of make-up. When we see a shot of the makeup head on, one can see two lipsticks at the far left corner of the case. When we see a shot of the case from behind, the lipstick is now at the right corner of the case.
Continuity mistake: When CC takes the pile of showgirl resumes from Maxwell in the office, she holds them with both hands. When the shot changes, she is holding them with one arm under the pile and the other hand leafing through them.
Continuity mistake: As Fran, Val and Maxwell are preparing to go out on the town, Maxwell's arms are hanging at his side. When the shot changes and he says "Excuse me", his hands are suddenly in his pockets.
Other mistake: Pretending to be Max's assistant, Fran dials a number for Bernadette Peters. The conversation is on speaker phone. The assistant says "one moment please." Niles and Fran continue talking and Maxwell comes in. Fran and Niles sheepishly hurry out of the room. Notice how, this whole time, Fran never touched the phone again to turn the phone off. So Max would hear Bernadette Peters and actually figure out Niles and Fran's plan before the episode's even halfway over.
Continuity mistake: In the second gym scene, while Fran is talking to The Gym Teacher, Maggie's arms change from being crossed to hanging at her side between shots.
Continuity mistake: When CC and Maxwell arrive at the wedding, CC has no scarf around her neck. When the scene cuts to her shortly after arriving there is a large brightly-coloured scarf around her neck, and two shots later it has disappeared again.
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.