But when he was 22 months old, his parents Jade and Bronwyn Maguire noticed he had become unsteady on his feet.
The active toddler was becoming reluctant to run or climb, his limbs started to shake, and he soon stopped walking altogether.
Doctors diagnosed him with an atypical teratoid rhabdoid tumour.
Bryn had two brain surgeries over the next two days.
He then completed two rounds of induction chemotherapy and three high-intensity stem cell returns after a transfer to Christchurch Hospital.
While there, Bryn and his parents stayed at the Ronald McDonald House where they received first-rate support.
The Kaka Point family then travelled to the United States where Bryn had seven weeks of proton therapy.
Since then, the tumour has not returned and Bryn only needs to have surveillance MRIs three times a year.
"He’s just like your average 4-year-old boy — it’s amazing," Mrs Maguire said.
"It’s such a privilege to be his parents. He’s such a cool wee dude."
Last night, she recounted the experience — particularly the support they received from Ronald McDonald House — to hundreds of people gathered at the Dunedin Town Hall for the Dunedin Supper Club live auction.
The event raised more than $450,000 for a Ronald McDonald House to be built in Dunedin.
Of that amount, $100,000 was donated by McDonald’s Dunedin franchisees Eterei and Justin Stonelake.
Mrs Maguire was grateful to all those who supported the fundraiser.
"Ronald McDonald House is such a valuable asset and it would have been impossible for us without them.
"To have one in Dunedin will be such a huge thing — it will relieve so much stress for parents."
