The son was taken to hospital in a critical condition, while the mother had less serious stab wounds to her head and body.
A year after the violent attack, Ngatama James Kaienua was found guilty of aggravated wounding and assault with intent to rob following a High Court trial earlier this year. He was jailed for 14 years.
The 28-year-old never entered the dairy, but kept watch outside while a 16-year-old went inside the dairy with a kitchen knife.
A local resident said only days earlier nearby Crescent Dairy had also been ram-raided.