Haddin, who struck 118 against England in the second Ashes Test at Adelaide Oval on Friday, said the health scare gave him a new outlook on cricket.
"It just showed me it was just a game," Haddin said.
Haddin was on tour in the West Indies in March last year when his then 17-month-old daughter Mia fell ill.
She was diagnosed with neuroblastoma, a form of cancer most common in infants.
Haddin returned to Australia, and he didn't play Test cricket again for a year, losing his status as first-choice wicketkeeper to Matthew Wade.
For much of his time on the outer, Haddin barely thought about cricket as Mia underwent treatment.
Haddin or his wife Karina would sleep at Mia's side in a Sydney hospital, while the other cared for their eldest child Zac and baby Hugo.
Mia's recovery coincided with Haddin's revival as a Test cricketer - he won another Test cap in March this year and was then named vice-captain for the winter Ashes tour.
Haddin's children watched him make a crucial 94 in Australia's series-opening crushing of England in Brisbane.
But he was glad his family weren't in Adelaide to witness his ton in the second Test, fearing his emotions would spill over.
"I'm pretty lucky I didn't score that hundred up in Brisbane when all my kids were there. I'm pretty relieved that I got it here when they're not here," he said.
Haddin admitted he was lucky to reach the milestone: he was dropped on five, and caught behind from a no-ball when on 51.
"You need to have luck in this game," the 36-year-old said.
"You can do all the technique work that you want but everyone needs luck in this game and I had my fair share."
His new-found perspective on cricket also helped.
"It's the state of mind. I'm pretty comfortable with where my game is at," he said.
"I'm enjoying being part of this team ... just enjoying my cricket."
BRAD HADDIN'S AUSTRALIAN RESURGENCE:
TEST BATTING CAREER
* May 2008 to January 2012
Matches: 43. Runs: 2257. Average: 35.82. Centuries: 3. Half-centuries: 10
* March 2013 to current
Matches: 8. Runs: 522. Average 37.28. Centuries: 1. Half-centuries: 4
Matches: 51. Runs: 2779. Average: 36.09. Centuries: 4. Half-centuries: 14