'Nanny McPhee' is a good movie in its own right, not merely as a kid's movie, or an art movie. Emma Thompson keeps on amazing us all with her screen writing (she is an Oscar winner for that, after all!), and her acting (ditto on the awards). Nanny McPhee is weird, to be sure--- but not just weird for weird's sake, such as a Tim Burton movie. Rather, the weirdness seems to take real life issues, and issues relating to parenting, and turn them around artistically into genuine entertainment.
The cast is stupendous. Colin Firth, great as always. The very pleasant surprise for me was Angela Lansbury. She must be 111 by now--- she was already a big Hollywood star back in 1941, after all. But here she played a classic old eccentric English character, SORT OF in the Margaret Rutherford vein, but unique, fresh, and amazing in its own right. It took me half an hour to place Lansbury, her character was so spot-on, and so wonderful. Her presence in the movie is a treat, in and of itself.
Children's movies have their own criteria for judgement, of course. But sadly, often kid movies are judged favorably if they posses a certain type of 'fairy-tale-ness', even if the movie is otherwise a load of crap. Like the some Tim Burton movies, in my humble opinion, or to some extent, even the recent Willy Wonka effort--- 'Charlie and the Chocolate Factory'. That movie was 'ok', but was substantially dark and creepy, as is most of Roald Dahl's work. But he smacks of Kid Movie Heaven, so critics and parents seem to praise his stuff irrespective of its true quality. Anyway, that's my view.
'Nanny McPhee' is light, airy, and very positive. As well as being a cracker of a movie. I would take my kids to it. I think the message for kids is overall positive, and something parents could be comfortable with exposing their children to.