The cash-only event will run from 11am-2pm, with $5 entry for kids aged 1-13. Adults and infants get in free.
Kids' activities will include an Easter egg competition, rock painting, nail art, craft tables, bouncy castles, train and pony rides, a baby shark dance competition and face painting.
There will also be plenty of food and spot prizes and best-dressed prizes will be awarded.
In another family fundraiser, Harris' cousin Haze Kopa is offering a special deal on tattoos and haircuts.
Anyone who visits his shop Tuturu Toi, at 152 Broadway in Kaikohe, between Monday, April 22, and Saturday, April 27, will be able to get a $100 tattoo or a haircut for $20. More than 100 tattoo designs will be available.
All proceeds from the Easter and tattoo/haircut fundraisers will go to the family's Givealittle campaign.
Spokeswoman Ruby Grace said Harris had a rough time last week but was doing well considering he was almost halfway through a 12-round course of chemotherapy.
So far the family has raised more than $42,000. To donate go to givealittle.co.nz/cause/from-graduation-to-hospital-gown.