Charn, who is the couple's fourth child, would not have survived without blood transfusions.
"Because he was so little, he couldn't make his own red blood cells," Ms Lee-Tuafale said.
"If I held both hands together, he would fit with only his limbs hanging out. He didn't have the strength to make his own. They continuously had to top him up."
Charn, who was in Auckland City Hospital's neonatal intensive care unit during his first four months, also received transfusions while undergoing operations for a faulty heart valve and bowel infection.
"We're just so grateful to the blood service, to all the services," Ms Lee-Tuafale said.
Around this time, the family also found out that Charn was suffering from brain bleeds, meaning he could have serious developmental problems as he grew due to brain damage.
"It was severe enough for them to warrant them asking us whether we wanted to continue with the life support."
While Ms Lee-Tuafale and her husband were "very close to letting him go", the pair decided against it. "Once he came home and was over being sick, so probably at about a year and a half when we were finally out of hospital, then we could actually just sit there and notice he could understand us when we talked to him."
Charn does not have full strength on the left side of his body because of brain damage.
However his older siblings - Troy, Paige and Marnei, aged 10, 9 and 4 respectively - help him around the house.
He also suffers from hydrocephalus and will continue to work with various therapists to help his development.
"They're all helping him to catch up," Ms Lee-Tuafale said.
Global appeal
World Blood Donor Day: Friday, June 12
• This year's theme is Safe Blood for Safe Motherhood.
• In New Zealand there were 58,717 registered births last year.
• Almost 12,000 units of blood and blood products were used by mums and newborn babies across the country last year.
• 7 % of all red cells donated in New Zealand are given to mothers and babies.
• 6753 women last year received 8355 vials of Anti-D, a blood product made from plasma.
Source: New Zealand Blood Service