Their small community, which is just outside of Whangarei, has been rallying around the family after the devastating loss.
A family friend of the Halfords said his parents, Deborah and Luke Halford, were heartbroken.
"He was one of six children, she's got five more and she's got another baby on the way so it's pretty tough."
She said the accident seemed to be the result of a misstep, and Declan was normally a good tree climber.
"He was just out doing what boys do. We're both quite outdoorsy people and we encourage our children to be outdoors taking risks.
"He was a very confident climber and he was usually outdoors doing something. It was just a horrible accident."
The family had "amazing support" from the community, she said.
Another family friend in the community set up a Givealittle page to assist with funeral costs.