One of the first things we did when the big girls were about 4 and 5 was to go on nature walks. We would go for a walk around the block, or to the local park, and pick up different leaves or cones to bring home for identification. We would also try to identify trees by their leaves, or the birds and insects at the park and in our backyard. If you have access to a good beach, go and look at shells and try to identify them. Sometimes we would draw our finds in our nature books, but almost always we would look them up in our nature books.
Here are some helpful New Zealand nature books for identification of New Zealand flora and fauna:
This is just one of a series of pocket guides to New Zealand wildlife. We own this one, as well as one on native trees and shrubs, and one on New Zealand birds. They are great for identifying common species, not just natives.
We have many more books on NZ nature, many of which I have picked up at library book sales for just a few dollars.
So get out there and enjoy the beautiful natural world that God has given us here in New Zealand! Your children will love it, and I believe, they will have a life-long love and interest in God's creation.