The paddock, which usually grazes sheep the rest of the year, backs on to the black sand beach and the water is perfect for swimming.
The great-grandparents, married for 58 years, don't take bookings but have never had to turn anyone away.
The only rule is that the campervans must be self-contained, as there are no ablution blocks, and they ask for a $10 a night fee, giving the money to local charities including Surf Life Saving and health care groups. Last year seven were given about $250 each.
The stunning location draws people back and in February they have agreed to hold a wedding on the property of a couple who spent their childhood holidays at the spot.
While some people stay for only a few days, others make it home for several months over summer.
Mr Simpson's father, Henry, started letting campers pitch tents 80 years ago. Then, the 390ha farm was one of only two properties on the beach.
Today, it's a popular holiday spot scattered with holiday homes.
"The front paddock just lends itself to holiday makers and my father didn't mind them coming in," Mr Simpson said.
"When it started there were only a few tents a year and it snowballed. And after a few years it was chockablock.
"As kids we always looked forward to Christmas because there would be a few people around."
Auckland man Richard Wilson first came camping with his family when he was 7 in 1955, and has returned every year.
He has become firm friends with the Simpsons and he and wife Jackie arrive a week before Christmas to set up a tent in their favourite spot near the end of the paddock.
His children grew up having beach holidays in the paddock and now Mr Wilson's 21-month-old granddaughter, Emma, goes with them.
"It's just a very special place for me. It's just magical."
He said there was a real community feel and there was always campervan hopping on New Year's Eve as the campers cracked open a few beers and celebrated the start of another year.
