"Mum's a bit of a practical joker, so when she phoned me at work to say we'd won the big one, I thought 'yeah right'," they said.
"It's not until I realised that she was actually in the Lotto shop that I started to believe her."
The family, who wish to remain anonymous, are regular Lotto players and have had only a few small wins before.
"It's still a bit hard to believe at times. But we're starting to think about new houses and new cars and all those exciting things," the family spokesman said.
"And we've always dreamed of travelling - now it's a case of deciding where we actually want to go."
The winning ticket was sold at Redwood Lotto in Blenheim, which had previously sold six Lotto First Division winning tickets.
The Powerball winning streak continued this weekend, with a Gisborne local winning the top prize of $6.3 million. The ticket was bought from Elgin Four Square in Gisborne.