Where: Theaters everywhere.

When: Opens today.

Rating: PG for mild thematic elements, some rude humor and brief language.

Running time: 97 minutes.

Bottom line: The anti-Mary Poppins keeps house in this charmingly manic little movie.

It may be one of the last socially acceptable prejudices that we tolerate whimsy in higher-concentrated doses from the British than from anybody else. That's one reason - perhaps the only reason - the cluttered children's fairy tale "Nanny McPhee" works when, by all rights, it shouldn't.

Emma Thompson plays the title character, a magical nanny who joins the Brown family at the most opportune moment. Mr. Brown (Colin Firth), a widower, cannot rein in his seven unruly children, who have driven away 17 nannies. Only Mr. Brown's maid, Evangeline (Kelly MacDonald, from "Gosford Park"), can abide them - but, then, she also has a secret crush on Mr. Brown.

The kids, led by the eldest, Simon (Thomas Sangster, the cutie from "Love Actually"), also aim to drive away any potential seat-fillers for their mother - without knowing that Mr. Brown will be cut off from his rich in-law, Great Aunt Adelaide (Angela Lansbury), if he doesn't wed soon.

Nanny McPhee arrives, and is (as Thompson has said in interviews) the anti-Mary Poppins: Rather than bringing spontaneity to an overly disciplined family, she brings discipline to an unruly group of siblings. But she does it from love: "When you need me but do not want me, then I must stay. When you want me but no longer need me, then I have to go."

Thompson, who also wrote the screenplay (her first since her Oscar-winning turn for "Sense and Sensibility"), is clearly having a ball playing Nanny McPhee, burying her face under a false nose and multiple warts. (The facial deformities factor into the story, but it would be rude to reveal how.) Her script is understatedly macabre, sort of what "Lemony Snicket's A Series of Unfortunate Events" tried and failed to be.

The script's wry humor survives even the hambone directing of Kirk Jones ("Waking Ned Devine"), who amps up the performances and the color scheme to cartoony extremes. Even when Jones' direction is at its most manic, Thompson - as writer and on-set nanny - remains a delightfully calm island amid the chaos.

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