Emma Thompson won't be winning another adapted-screenplay Oscar for her sophomore script, but she has written a most enjoyable combo of familiar plots and themes for the film of Nanny McPhee. Based very, very loosely on Christianna Brand's Nurse Matilda books, it takes one of the most commercially trite foundations for kiddy comedies — that of the unsinkable nanny — and adds the current safe bet for family films: magic.

The result is an unnecessary but satisfying mix of light and dark comedy that should come as no surprise from Waking Ned Devine director Kirk Jones. Finally following up his loveable debut after seven years, he continues his ability to make death a pretty funny concept. Devine begins with an old man croaking suddenly after winning the lottery; McPhee tops it with six children eating a baby.  

 
Don't worry, they actually only appear to be eating a baby. In an effort to get rid of yet another nanny, the incorrigible Brown siblings stage an unseemly act of cannibalism, using chicken bones and the clothing of their little sister. It is a deed that is impossible not to respect, and the kids, adorable but not precocious, clever without a lack of innocence, are impossible not to love. 

Their father, mortician Cedric Brown (Colin Firth), has a hard time showing his affection, however, and that is part of the reason his offspring have turned into enfants terribles. Ever since the death of his wife, their mother, he has been simultaneously busy in mourning and in the search for a new bride, leaving no time for bedtime stories or cricket practice. He can't even give them the attention of proper authority or discipline, for if he doesn't remarry soon, his aunt-in-law, Adelaide (Angela Lansbury), will discontinue the allowance she gives him in order to support his seven children. 

Along comes Nanny McPhee (Thompson), an ugly sort of anti-Mary Poppins who may in fact be a witch. Rather than making chores fun and medicine sugary, she amplifies the children's troublemaking so that it makes trouble for them. When they fake sick with made up measles so they don't have to get up, Nanny McPhee curses them with an actual temperature and paralyzes them in their beds. After one day under her spells, they not only begin the road towards good manners and obedience, they discontinue further attempts to fool, undermine or dispose of their new governess. Eventually they even start to like her.

There must be enough tales, let alone films, involving a pack of mischievous brats who prank their babysitters or stepparents. The concept of misbehaving for unwanted authority figures has been the delight of children since the beginnings of storytelling. Sometimes in the movies kids are faced with a fearless new guardian, perhaps in the form of a singing nun, a singing enchantress, an amnesiac prima donna, a pro wrestler, or a Navy S.E.A.L., who tames and teaches the tykes while earning their love and trust, but I bet that by the end of many of these feel-good, forced-moral films, a lot of young audiences are wishing for more shenanigans.

Nanny McPhee never stops with the antics — though none of them better the savage introduction — even as the kids and their caretaker forge a bond. While the Brown lot is accepting Nanny McPhee into their hearts, they are given a new adversary. Mr. Brown decides to rush an engagement with the notorious hag and serial-bride Selma Quickly (Celia Imrie), who, consistent to the fairy tale formula, wants nothing to do with her future step-kids and everything to do with Cedric's money. Meanwhile, their great-aunt Adelaide remains an enemy, as she threatens to seize and foster one of them so as to relieve part of her nephew-in-law's financial burdens. Between the two horrendous ladies, there are plenty of frogs, worm sandwiches, green slime, and barnyard animals to go around for young viewers to celebrate.

While the little ones applaud defiance, there are a number of things for the grown-ups to appreciate with Nanny McPhee. Taking a minor cue from the best of the Britain-based fantasies like the Harry Potter series, the production has assembled a brilliant crop of actors, which includes Kelly Macdonald and Imelda Staunton as the Brown's maid and cook, respectively. No role is too small for a seasoned thespian, and therefore no character is devoid of a memorable presence. Firth makes up for his appearance as an inexperienced father in What a Girl Wants by playing even more unknowing and more hopeless. And Lansbury, prostheticized and acting blind as a bat, gives a daft performance that is worth the twenty-year wait for her return to film.

Nanny McPhee really works, though, despite all of its common plots and ideas, because it stays true to storybook conventions that have never and will never get old. This includes archetypes such as the fairy godmother, wicked stepmother, transformed maidens, as well as a slight cruelty towards children. On top of that, Jones gets the tone of the story completely right, blending perfectly his talents for simplicity, wit, charm, slapstick and black humor. The movie is everything that Lemony Snicket's A Series of Unfortunate Events should have been, although it doesn't beat that film's production design.

Nanny McPhee lives by one principle, which she dictates to the Browns: "When you need me, but do not want me, I will stay. When you want me, but do not need me, then I have to go." As applied to the film, this could be unfortunate, for if anyone wants a sequel to Nanny McPhee, but does not need one, they may not get their wish.