Harrison spent several months in and out of Auckland's Starship children's hospital, braving debilitating chemotherapy and radiotherapy.
"A little prick in the arm is insignificant to what he went through," Mrs Mundy said.
"During his treatment for cancer, he received many blood transfusions so we just thought that today was a great day to honour him and to do something good."
She said it had taken up until now to find a fitting way to honour her son.
"I think we have kept to ourselves a little bit on February 16, but as time goes on it's nice to spend the day surrounded by our friends and family."
Raising awareness for blood donation centres is also important to the Mundys.
"We hear a lot about road accidents needing loads of blood but also places like Starship, they go through truckloads of blood when they're treating the little ones up there, especially for us on the cancer ward," Mr Mundy said.
"It's blood that is well needed and helps out," he said.
The Mundys and their supporters formed Team Red for Harrison as part of the New Zealand Blood Service's group blood donation programme called Team Red.
Through the programme, the Mundys will be able to track how many friends and family members donate blood in Harrison's name and even see where the blood gets donated.
"We would like to encourage more people to donate blood. There are so many sick little children out there and that is a real motivating factor for us," Mrs Mundy said.
"He [Harrison] would have been really proud of us."
New Zealand Blood Service is a not-for-profit crown entity responsible for the collection, processing, testing and storage and distribution of all blood and blood products nationwide.
The service relies on voluntary and non-remunerated blood donations from individuals around the country in order to provide a constant supply of precious blood and blood products used by our health services to save thousands of lives.
The need for donors is constant – 3000 donations must be collected every week nationally, and the service is always working to maintain and grow its register of donors to make this possible.
For more information on how to donate visit https://www.nzblood.co.nz/