One of the problems with filming the scene with the piglets running away from the children was that the little pigs enjoyed being caught and cuddled, so they were very disinclined to run away.
For the scene where Nanny McPhee (Dame Emma Thompson) effectively takes over the unruly children, making them apparently start hurting themselves, a mime artist was brought in to train the children in the arts of mime and puppeteering. The scene took three weeks to rehearse.
Originally, it appeared that Dame Emma Thompson would not be able to play "Professor Trelawney" again in Harry Potter and the Deathly Hallows: Part 2 (2011), due to her duties as writer and producer of this movie. However, filming wrapped on this movie prior to the end of shooting on Harry Potter, and shortly before the latter movie wrapped, she was able to return to film her scenes, along with cast-mates, Ralph Fiennes, Rhys Ifans, Dame Maggie Smith, and her own sister, Sophie Thompson.
The field of barley was grown for real in Buckinghamshire. Rhys Ifans had managed to hurt his ankle, delaying filming for two weeks. By the time they were ready to shoot, the barley had turned a beautiful bright yellow. If they had stuck to their original schedule, minus Ifans' accident, the field would have been green.
Director Susanna White wanted to make this movie as she loved the depiction of Mrs. Green as a modern independent woman, despite the movie being set during World War II.