He has been told he has 12 months to live.
"We are trying to extend that," said his daughter, Mrs Dennes.
"My Dad and Ceejay have an incredibly close relationship, they are always doing things together."
Mrs Dennes said her son came up with the idea after seeing an ad on TV showing a father who had shaved his hair off in support of his young son, who had cancer.
"Ceejay said 'I'd quite like to do that for Poppa' and I said 'yep, you can do that'."
Mrs Dennes helped Ceejay set up a fundraising page on givealittle.co.nz, a free crowd sourcing fundraiser website.
In just over a week, donations have been flooding in through the website and the community.
Mrs Dennes and Ceejay have been amazed at how much money has been donated and how fast it's happened.
"It's almost like it's gone viral, it's turned into quite a large thing.
"And it's all from one little boy that said 'I'd like to shave my head for Poppa'," said Mrs Dennes.
She said her father was quite humbled by his grandson's actions.
Ceejay's humanitarian nature may be in the blood.
"My Dad has spent years volunteering, he's a volunteer firefighter, he's the kind of guy that usually does things for other people," said Mrs Dennes.
"He keeps saying to Ceejay 'you're not going to shave all of your hair off are you?"'
He worries his head will get cold, she says.
She said cancer was not something her children were surprised about because of the nature of her job.
Boy shaves hair for Poppa
Mrs Dennes teaches children with illnesses, like cancer, at the Greytown branch of the Central Regional Health School.
The fundraiser has been a good distraction while Mr Smith is away getting treatment.
Ceejay will be getting his head shaved at the South Wairarapa Working Men's Club at 4.30pm, July 26. Mrs Dennes said he might get a "bit of Stan Walker design, something funky".
Donations can be made at www.givealittle.co.nz/cause/mopchop4poppa
There is also a collection bucket at R & B Motors Greytown.