NZeTA and visitor levy. Most visitors from visa-waiver countries, including the US and UK, need a New Zealand Electronic Travel Authority (NZeTA) before boarding and pay the International Visitor Conservation and Tourism Levy (IVL) with it. Australian citizens do not need one; check the visa rules for your passport before you fly.
Biosecurity declaration. Every traveler, children included, completes the New Zealand Traveller Declaration, ideally online before landing. Declare all food and used outdoor gear such as hiking boots, tents and fishing equipment: an undeclared risk item brings an instant NZ$400 fine, even by mistake.
Two terminals. International and domestic flights use separate terminals, so give your flight number and arrival terminal when you book, especially if you connect from a domestic flight.
Driving on the left. New Zealand drives on the left, and seat belts are required for every passenger.