In “Nanny McPhee Returns,” Emma Thompson stars as the magical nanny who appears when she's needed the most and wanted the least.

Nanny McPhee’s second foray onto the big screen is just a bit sweeter than the first. Sweet as in pickles, not sugar, because this movie isn’t afraid of alienating its audience by throwing in a little sour realism amid the magic.

Thanks to star Emma Thompson’s smart, appealing script, the mysterious babysitter with the grotesque face and no-nonsense ways once again delivers a welcome antidote to Disneyfied heroines.

This time, she descends upon the Green family’s muddy, chaotic farm, barely held together by a harried mom (Maggie Gyllenhaal, having the time of her life) raising three quarrelsome kids while her husband is away at war. When two rich, haughty cousins arrive via chauffeur, a pint-size class war breaks out, until Nanny McPhee — “small c, big P” she says, chin tucked into her neck — appears and teaches them five life lessons without them suspecting a thing.

Thompson, who won an Oscar for her adapted screenplay of Jane Austen’s “Sense and Sensibility,” has managed to spin a story that can engage both kindergartners and 9-year-olds. Poo jokes, pigs doing water ballet, baby elephants in the bedroom and slapstick abound, as do great performances. Rhys Ifans is barely recognizable as a double-crossing uncle, Maggie Smith is delightful as an eccentric shopkeeper, Ralph Fiennes turns in an intense cameo as the cousins’ distant, forbidding father, and tween actor Eros Vlahos plays cousin Cyril like a miniature Oscar Wilde.

Parents may find themselves checking the time on their cell phones less often than usual. But be warned: After seeing “Nanny McPhee Returns,” your kids may start clamoring for egg-and-cress sandwiches, ginger beer, drawers filled with treacle and — of course — a supernatural nanny who says, “When you need me, but don’t want me, then I must stay. When you want me, but don’t need me, then I must go.”

“Nanny McPhee Returns”

109 minutes

PG, for rude humor, some language and mild thematic elements