"The person you need is Nanny McPhee." Or so says the disembodied voice coming from the mail slot when Mr. Brown (Colin Firth, "Bridget Jones's Diary") comes to request an 18th nanny for his children. And so Nanny McPhee (Emma Thompson, "Harry Potter and the Prisoner of Azkaban") is introduced as the magical person who can solve one man's problem with his naughty children.

The premise feels familiar enough. Based on the "Nurse Matilda" books, "Nanny McPhee" seems to be a Disney movie complete with overworked father, magic and bright colors.

But "Nanny McPhee" is Mary Poppins without that spoonful of sugar. It's a darker story, where the actions of children hold life-altering consequences; father and son heart-to-hearts are held in a morgue, and the threat of separation comes in the guise of charity.

Besides, Nanny McPhee is certainly no youthful beauty. Instead of Julie Andrews and her magic bag of tricks to save the day, there's Thompson's snaggle-tooth, wart-faced McPhee who carries a menacing cane. She arrives to care for the seven Brown children, led by Simon (Thomas Sangster, "Love Actually") and their father. Mr. Brown's troubles are not just domestic. He must marry by the end of the month or his Great Aunt Adelaide (Angela Lansbury, TV's "Murder, She Wrote") will take away his stipend, which would throw him in debtor's prison and separate the children.

The screenplay, written by Thompson, is scattered but effective. There's few children who won't get a kick out of the food-fight scene or the Brown children's mischief. And adults will pick up the references to class distinctions and the power of rich familial relations. It's fitting as both Thompson and Firth have preformed in adaptations of Jane Austen's work, among the original documentarians of manners.

But while the screenplay strives to appeal to both types of audiences, its inability to satisfy fully either the old or the young set ultimately disappoints.

Still, what the movie lacks in script, it makes up for in character. The cast fits easily into this Victorian fairytale, and both Thompson and Lansbury know how to work their prosthetic noses. The antics of the children are lively, though often misguided, and it's nice to see the children learn their lessons at the end of each trial. Nanny McPhee is so pleased to see them get the point that with every lesson learned, one of her deformities disappears. The computer animations might seem a little rough around the edges to a parent's eye, but the kids aren't going to critique a dancing donkey.

"Nanny McPhee" creates a vibrant world, but no color can mask its dark undertones. It's jarring to see children smack the cook over the head with a saucepan or send their dolls to the guillotine. The methods Nanny McPhee uses to teach her lessons are not so gracious, either; she's tough because it's the only way to get through to the children. Though the movie ties all the conflicts up in a clean and contrived little bow, Thompson's performance is magical enough to elevate the entire production. She's splendid in the role, and it's good to know that when Marry Poppins can't do the trick, you can always call upon Nanny McPhee.

Rating: 3 out of 5 stars