Enjoying the indoor game's social nature as well as its fast-paced play, the Tauranga duo found fresh inspiration on discovering that a chance to test themselves against the world's top young talent was up for grabs.
"We only realised two weeks before the junior provincials that a national team would be going to the world juniors, we got an email about it," McKenzie says.
"It sounded amazing, I spoke to my parents and they said they'd put my name forward to be considered for selection.
"It was pretty overwhelming to be picked.
"When I was named in the team at Wellington and had to walk to the front of the stage, I felt a bit wobbly."
A student at Mount College, McKenzie finds cricket's indoor offshoot a refreshing complement to the outdoor summer game.
"It's great to get out there and get active. You're meeting new people and having fun."
A strong batsman who customarily comes in at second drop for his Mount Cricket Club junior outdoor side in summer, McKenzie is also a frontrunner for the wicketkeeping role at the junior indoor worlds.
Coulter, who attends Tauranga Boys' College, was also buzzing at being chosen to represent his country.
"It's pretty exciting. My name got read out first, it felt amazing. I haven't been up for any prizes in sport before."
The duo got their first taste of national rep training two weekends ago with a five-hour team session with the side's coach Mark Horan in Auckland.
"It was quite tough but Mark is really good," Coulter says. "He got us bowling around the wicket, putting the ball into the batsman's body, making it harder to hit."
Attending Papamoa's Tahatai Coast primary school until this year, McKenzie was in the Bay of Plenty Coastlands under-12 outdoor side at the Northern Districts primary schools tournament in Hamilton last December, and has also played for Te Puke/Mount Maunganui teams at the Wanganui Cricket Festival three summers in a row.
Coulter has played for the Tauranga Boys' College Year 9 outdoor team in the city's Saturday competition and was named in a Western Bay of Plenty age-group selection.
New Zealand masters indoor player Darren Bidois has been sharing his expertise with the Tauranga pair, coaching one-on-one with them a couple of times a week at Action Indoor Sports.
Indispensable in developing the two boys' indoor skills is Action Indoor Sports Bay of Plenty director Andrew Templer, who has coached and encouraged the promising duo from their early days. There's no doubting Coulter and McKenzie's passion for the indoor format, Templer says.
"Whenever there are games on they are involved, they're soon addicted to it."
The pair have one more training session in Auckland with the 10-strong side before heading to Johannesburg, and they have also been fronting in the Bay of Plenty under-19 indoor team recently to further hone their skills.
The $4000 cost of the South Africa sojourn was the reason parents had to expressly enter their kids for consideration.
This Sunday McKenzie and Coulter's worlds foray will get a boost with a six-a-side fundraising tournament at Action Indoor Sports Centre, aiming to raise $1000 towards each of the pair's expenses. Coulter's mum Michelle says local businesses including Papamoa Pak'nSave and Bay Precision Panel and Paint have provided valuable support, along with Mount Maunganui Cricket Club.