I wasn't too keen on seeing this because i thought it would be a very kid movie, but i'm glad i did. The actors are good, especially Thomas Sangster (Simon). I just loved him! Emma Thompson can change the slightest turning of her head and a mumbled 'hm' into so many things. It is a very cute story, heartwarming sometimes, thought-provoking other times, and funny the rest of the time. The special effects, i think, were perfect. Just enough to show that it was magic, but it wasn't over done, as in some other 'magical' movies.
The only thing i did not like about the movie was the fact that the ending was pretty obvious, but it is very hard to make a fairy tale with a twist ending. We never do find out anything about Nanny McPhee, which is sort of the point, i think. She is just THERE. Doesn't matter why or how. The movie isn't about HER as the person - its about what she brings about.
I definitely recommend seeing this movie, no matter how old you are.