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.
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 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.
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.
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.