Nanny McPhee
(2005)

Nanny McPhee (Emma Thompson) succeeds in civilizing the children, Evangeline (Kelly McDonald) and Mr. Brown (Colin Firth) get married, and Nanny McPhee leaves when she is no longer needed, a la Mary Poppins.

And yes, that is Derek Jacobi as Mr. Brown's assistant.

Thanks Jigsaw!

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Read more about this film at The Internet Movie Database.