"All the other things, like my 7-year-old's iPad and the few T-shirts they took don't matter, all we care about is the cap.
"He loved that cap, he always wore it during his treatments," Mr Tahuriorangi said through tears.
"We wanted to give our son a headstone he deserved, a headstone that represented what his life was like, that's why we wanted this cap to be a part of that."
Mrs Tahuriorangi posted an impassioned plea on social media for the cap to be returned which quickly went viral, being shared more than 1500 times.
"We moved to Brisbane nine years ago but it was always our intention to bring Kahu back home to live if he got better or to bury him," Mr Tahuriorangi said.
"It hurts coming back to our hometown and seeing what it has become . . . It would be a small miracle if we did get the cap back but we're hoping human guilt will play on those who took it."
He said while his family had been hurt by the theft, they had also been blown away with the response on social media.
Mrs Tahuriorangi said her son was a "beautiful boy" who only wanted to be free from the rhabdomyosarcoma he was diagnosed with.
She said because of the type of cancer her son had, his treatment was aggressive, but "he was so strong through it all".
"We all thought because he was doing so well that he would fight it."
She said during his treatment and as he lost his hair, the cap became a second skin to him.
"The type or style had nothing to do with why he wore it all the time. When we packed his suitcase to be buried with him, for some reason we'd forgotten about this one cap.
"A month after his passing I decided to clean my wardrobe out of the blue and found it sitting right there like it was a sign.
"Whether he wanted me to find It I don't know but it was so good to have it with us. Caps were just a part of who he was."
The family are returning to Australia tomorrow but would still like to hear from anyone with information about the cap.