Cedric Brown (Colin Firth) is a widower and a father of seven unruly kids who keep driving away their nannies one after another. Nanny #17 runs away screaming after the kids make her think they have cooked and eaten their youngest sister. After that, the nanny agency closes its doors in Mr. Brown's face. As he stands there hopeless, he hears a mysterious voice that tells him he needs Nanny McPhee. However, no information is provided regarding how to contact this nanny. She shows up on Mr. Brown's doorstep shortly afterwards, startling him with her ugly appearance. Nanny McPhee (Emma Thompson) is adorned with a big nose, warts, and a bucktooth. However, she seems to know her job, and with the help of a magic walking stick soon begins to teach the kids some valuable lessons. As the kids learn those lessons, the nanny's appearance mysteriously improves - until she is the Emma Thompson we know and love.
The movie targets kids, so most of the humor is juvenile. There are all kinds of pranks, food fights, and unimaginable messes made; there is also the infamous dancing donkey scene, criticized by most adult viewers. While I did not care for that stuff, either, I greatly enjoyed the actors. Colin Firth is very good; Angela Lansbury is hilarious as Mr. Brown's wealthy Aunt Adelaide who insists that he remarries. Celia Imrie plays Mrs. Quickly, a ridiculous widow he is forced to court; she turns out to be a villain in disguise, but we suspect it from the start. Imelda Staunton also provides some good laughs as Mrs. Blathersick, the cook, who thinks that the kids will never dare to invade her kitchen (wrong!).