Parents devastated after being told their son might not survive

The parents of a little boy who nearly died have spoken about the heartbreaking moment doctors told them their son may not live.

Brodie Marshall was just 17 days old when his lungs filled with a toxic carbon dioxide and he stopped breathing.

Chained to tubes and wires, his lungs were failing him. Brodie was diagnosed with congenital lobar emphysema – a rare respiratory disorder where air can enter the lungs but cannot escape.

Brodie's left lung had inflated so much it was pushing his heart to the right, with the right lung squeezed in.

"The only question I remember asking was 'is my son going to die?'" Brodie's mother, Vikki, told 9NEWS.

"Their reply was at this stage we don't know.'"

That questioned remained unanswered for two weeks while the young parents clung tightly to their baby boy in hospital.

But the night before he was set to undergo life-changing surgery, Brodie suddenly stopped breathing.

"It was the worst five minutes of my life," Mr Marshall said.

"To see 20 people working on your baby, us standing out looking through a window absolutely helpless.

"It's terrifying."

After beginning to breathe again, Brodie underwent a delicate surgery at Monash Children’s Hospital in Melbourne to remove half his lung.

A year on, the 18-month-old is healthy and thriving and his thankful parents want to give back to the team who saved their son.

They will join hundreds of people for the annual Walk for Monash Children's Hospital. The goal of the walk is to raise more than $100,000.

"Our story could be incredibly different," Ms Marshall said.

"And to think how close we were to losing him, it's been an incredible eye opener."