"We knew we needed to take him home and a few hours later he passed away. He saved us the heartache of being in hospital and from us thinking it was some adverse effect of the transfusion."
The Topperwiens said when they think of their only child they feel calm.
"When we think of ourselves we are heartbroken beyond description but he gave us a lifetime of memories to keep us going."
The couple have made a commitment to setting up a charity in Chace's name.
"All those traits he had will ensure that Chace continues to have an impact on this world - bravery, resilience, laughter, strength and hope and an undeniable positivity."
It had been a strange and surreal weekend, they said.
"We expected rain and thunderstorms to reflect our sadness but of course being Chace, it's been beautiful weather, calm seas and no wind. Our boy must have been reminding us that he is okay. He is resting and he is on his way to play with his great Kokos. I can hear him say 'It's okay mummy, here I'll wipe your tears' in his husky little voice."
Mr Topperwien said they had organised a screenprinted coffin covered with pictures of Chace's favourite places, including Ohope beach.
He said they would cremate Chace and one day his ashes would be scattered at sea " ... where he had the most fun, in the water".
Chace was diagnosed with a rare and aggressive form of acute myeloid leukaemia on his second birthday, in March last year. Mr and Mrs Topperwien raised money for treatment and even travelled to an overseas drug trial in a last-ditch attempt to save his life.
Their plight attracted the attention of wealthy expatriates Owen Glenn and Eric Watson, who each gave $25,000 to help pay for the expensive trial.
Mr Topperwien said the couple had had their moments since Chace died but they thought of him running free.
"It's hard but you just have to think he's not in any more pain. He's probably running around, not just sitting because he couldn't walk any more."
