His mother, Tracy, knows it could have been all too different.
Hamish was born with biliary atresia, a condition where the bile duct between the liver and the small intestine does not form. When he was 3 months old his parents were told the worst: without a new liver he would die within weeks.
Mrs Crossan (37) said there was no question she take the barrage of tests to see if she could donate part of her own liver to her son.
"The chances of a liver from a deceased donor becoming available in time were very slim [so] it wasn't a difficult decision to make at all ... Gavin, my husband and Hamish's father, would have done it too if I hadn't been a match," she said on Wednesday.
The Crossans made history when the transplant was carried out at the New Zealand Liver Transplant Unit at Auckland Hospital on July 24, 2007.
Hamish, then 5 and a-half months old, was the youngest New Zealander to receive a new liver and Mrs Crossan was the first live donor mother.
Her operation was performed by Prof John McCall while Hamish's was done by another surgeon in a separate operating theatre.
Mrs Crossan said she would always be grateful for Prof McCall and his colleagues.
"They are all amazing. They care so much and are all so personable. We are so lucky in New Zealand to have guys like them."
