The first word 18-month-old Sam Tomlinson learned to say was "Mum" - two days after she died.

Two months on, he still asks for her before he goes to sleep.

Nadine Tomlinson, 33, and her 3-year-old son Angus were trapped inside a tractor which lost control and slipped into a dam on the family's farm in Waihemo, near Dunback in North Otago, on September 30.

The accident also claimed the life of her and her husband Scott's unborn son.

"There is a big hole in our lives. Sam and I talk about Nadine all the time we make her a vivid memory with photos," Scott Tomlinson told the Weekend Herald.

"I'm pretty blunt and upfront about what happened to Nadine and Angus. We live the moment and watch all the videos. Sam knows what happened.

"He misses his brother a lot and climbed into his coffin - he's seen the video of that. I filmed the funeral and will show it to him once he is old enough to understand."

Nadine and Scott, who were both raised on farms, met at Lincoln University where they both majored in agriculture.

After shepherding in the North Island for several years, Nadine headed overseas for her OE. On return, she joined Balance Agri-Nutrients as a field consultant.

She married Scott at Tekapo 4-and-a-half years ago and moved to Dunback to start their "farming dream".

Tomlinson's days are busy juggling parental duties and working on the farm alone.

His working day starts before Sam wakes up at 6am and ends after Sam finishes daycare.

And driving past the crash site every day is not only challenging but a cruel reminder of what he has been lost.

"Straight after the accident I was okay, I thought it was going to give me strength but after a week or two it got tough," he said.

"I'm still not sure on our mid-term, long-term future about me staying here and trying to fulfil Nadine's dream. The memories are too painful and raw. Some days I get motivation from them but other days it goes the other way."

He was grateful for all the support he's received from family, friends and neighbours.

Last weekend they rallied together to help with riparian planting around the dam.

Ann Restieaux, Nadine's mother, praised Tomlinson's efforts to "fulfil Nadine's dream".

"The riparian strip around the dam was something Nadine was keen to do so he's gone the extra mile," she said.

"My son who is an engineer designed a memorial seat with stone steps leading up to it. Scott is such a toiler with a big heart. You couldn't wish for your daughter to be married to anyone nicer."

The family is hoping a WorkSafe NZ investigation will reveal what caused the accident on September 30.

Restieaux still can't figure out how Nadine, who was an "experienced" tractor driver ended up in the dam.

"It still breaks my heart how she fought to get out of the tractor," she said.

"As it was filling up with water she must have found a draw bar pin to break the door off the tractor. She tried to get her gumboots off because she knew they weren't good for swimming. So they got out of the cab but it was too much for them - they were overcome and were found behind the trailer so that was pretty awful."

Restieaux said her daughter was a "goer" and would've given it her best to save them both.

"She might have got out if she was on her own but having a wee fella there - she would never want to leave him behind. I mean you always protect your kids don't you?."

Tomlinson and Sam are spending Christmas day with Nadine's family in Clinton. But he isn't looking forward to this Christmas, the first without his wife and eldest son.

"We didn't stop much because it is a busy time on the farm but at least we had each other so we could try and make a Christmas atmosphere around the house. Now it's me and Sam, it's going to be tough to instil that happiness for him".

And every day he thinks of the son he will never meet.

"I keep that at the forefront of my mind at what stage she would be in the pregnancy. She was 16-weeks then so I figured by Christmas time she would be about 6-and-a-half months."