The pair were supposed to be caring for Moko at their Taupo home while his mother was in Starship hospital with her eldest child.
Instead, the pair tortured the 3-year-old until he could resist no more - he was pronounced dead on August 10 last year.
He was covered in bruises from head to toe and was broken internally. The official cause of death was multiple blunt force traumas.
Shailer and Haerewa encouraged each other's actions. They kicked, stomped and slapped him. They rubbed his own faeces in his face.
For four days Moko's last struggle dragged on until the couple eventually rang 111, saying the boy fell off a woodpile.
As the pair were sentenced in the Rotorua High Court, organised marches and rallies were held around the country to protest the plea bargaining which saw the murder charge dropped and replaced with manslaughter.
At the time, Attorney-General Christopher Finlayson said the murder charge was dropped as there was a significant risk Moko's torturers wouldn't be convicted if they headed to trial on a murder charge.
To prove murder, it would need to be proven beyond reasonable doubt that Moko's injuries were inflicted with murderous intent.
Shailer and Haerewa had a responsibility to get medical treatment for Moko, Mr Finlayson said. By failing to do so, they contributed to his death, in addition to causing his injuries.
The New Zealand Bar Association and Law Society also publicly expressed faith in the "robust" processes around downgrading charges.
But Jayne Walker, of the Sensible Sentencing Trust, says the rest of the country didn't buy it and ended up organising the marches after being blown away by the "phenomenal" response they received from Kiwis asking what they could do to help.
"The time and date were chosen to coincide with the time the killers were sentenced for manslaughter; not murder as we firmly believe they should have been. This was murder and of the very worst kind."
The Sensible Sentencing Trust created the Justice for Moko petition calling on Government to introduce a system under which a High Court judge must approve any arrangement under which any originally laid charge alleging murder is replaced by a lesser charge, with the judge empowered to order that a trial of the defendant[s] on the original charge proceed; and as a matter of urgency, make whatever law changes may be necessary to outlaw the practice of plea bargaining negotiations initiated by crown prosecutors.
Guest speakers at Thursday's march will include politicians Dennis O'Rourke from NZ First, Marama Fox of the Maori Party and Act leader David Seymour. Representatives from Green and Labour will also attend.
