Oliver will need to have multiple surgeries and treatment throughout his life.
After seeing the support his family received from Heart Kids, Day and his wife decided they wanted to give back.
"In Ward 23B in Starship, where heart kids are so capably looked after, we had plenty of time to think," he said.
"We decided that we wanted to do something to give back to the system that supports these children after they leave Starship and get back out into the community."
And so, the Chamberlain Owners' Group came up with the Heartland Tractor Trek.
Developed in Australia by Bob Chamberlain, the Chamberlain tractor went out of production in the 1980s, Day said.
The tractors can get up to speeds of 40 to 50km/h, but Day had heard of "all sorts of tricks being done" in Australia to achieve 75 to 80km/h.
"In fact in 1957, one was geared up to do 100km/h and drove around the Repco Round Australia Rally as the tail-end Charlie, and that's where it got its famous name from."
The trek will travel from Taranaki to Wellington and ferry to Picton. From there they will head to Rangiora to meet the rest of the trek participants.
The convoy will continue heading South and visit towns along the way, "to have a stretch and a breather," Day said.
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It will also be a chance to meet locals, schools and clubs and "do some bucket shaking" to increase awareness for Heart Kids, Day said.
"It's a lot of fun."
The trek will eventually arrive in Otago to be part of the three-day, Wheels at Wanaka event, before travelling north again to complete the journey in Rangiora.
"It's a fair old distance," Day said.
The trek and Heart Kids had "tremendous respect" for Wheels at Wanaka, after a conversation with founder Allan Dippie about "shaking buckets" turned into an offer to be the event's charity partner for 2021, Day said.
"The Heartland Tractor Trek highlight will be stopping at Wheels at Wanaka."
The aim of the Heartland Tractor Trek starts on March 25. So far just over $40,000 has been raised toward the $75,000 target.
To find out more, or to make a donation, head to Heartland Tractor Trek website.