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: When Fran and Maxwell are changing the baby's diaper in the kitchen, the baby "pees", but the pee shoots from the baby's chest.
The Nanny Behind the Man - S2-E18
Revealing mistake: When C.C tells Niles "Stay on your toes" he supposedly steps on her toes but it is clear that he does not get anywhere near her toes before she cries out in pain.
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.