Nanny McPhee is the spirit of the Brown childrens' mother
- Nanny McPhee had to disguise herself with the imperfections as a way to conceal her true identity. It would explain the way she talks to Aggie when she first tells them to go to bed. As well, it would explain why after her transformation, no one calls her Nanny McPhee. She also gives a nod to Mrs. Brown's chair.
The Nanny McPhee films take place in the Disney movie-verse, just further down the timeline.
- The extremely colourful first movie, to an almost absurd degree, and the vague location could place the film in the country several of the Disney films seem to take place in. In the second movie, the frequent references to a 'war' without actually identifying what war or even who the enemies are. the enemy plane that shows up in the second movie is actually labelled as Enemy Plane which would indicate that it takes place in the very vaguely defined Europe of the Disney Animated Canon.
Nanny McPhee is a Collective Identity...
- ...of possibly thousands of mystical nannies deployed whenever and wherever they are needed, only to dissipate after their job is done. Thanks to Celebrity Paradox, they all look like Emma Thompson to us, but in fact look like the ugliest possible thing to whichever family they are sent to, then leave looking like the most beautiful. The military system may be an indication of how long this has been going on - they are literally Older Than Feudalism.
Nanny McPhee knows Mary Poppins in some way or another.
- This one isn't even hard to imagine, they're both seemingly ageless magical nannies that show up when things are dire, have people who remember them from previous appearances in their life, and are very effective. Even if it's by reputation, they should know one another.
Nanny McPhee is a Fairy Godmother.
- McPhee is a member of The Fair Folk who was Intrigued by Humanity, and started to play magical benefactor to children in need. This did not sit well with her race. They decided she could be a nanny, but only if she bore two curses: Her ugliness, and the clause of her work: She can only stay with children who do not want her, but must leave whenever they grow to love her.
Miss Topsey and Miss Turvey are witches like Nanny McPhee.
- Miss Topsey and Miss Turvey display similar powers to Nanny McPhee throughout the sequel film: they are able to teleport, instantly change clothes, and retrieve items from nowhere. It is possible that whatever Nanny McPhee is (a fae, a witch, etc), Miss Topsey and Miss Turvey are the same thing only they use their powers maliciously instead of benevolently.
When Nanny McPhee says, "I'm a [organisation] nanny", that means she babysat for someone in that organisation before.Hence, "I'm an army nanny" and then later the soldier recognises her.