I don't know if I can describe a New Zealand accent. Having lived here for several years, it's sort of become 'the norm'. To my own ears, it is far less harsh than the Australian accent, though they are similar. Example: the word fish
NZ accent: Fush
Aus accent: Feesh

I prefer the softness of the 'u' to the harshness of the 'eee' sound that many Australians seem to have. But like in all places, there are variations. My own husband has very little twang to his accent, and is often mistaken for being British.

The girl and everyone in the movie is a New Zealander with New Zealand accents. But you must take into account that they are Maori, which alters their accent. Much like the way that a Mexican or African American person have varied American accents.

Yes, Edwina'sSecretary, it is totally appropriate for eighty year olds, as well as youngins. It's a great family movie.