The 16-month-old was rushed to hospital on June 23 around 7.30pm, however, he was pronounced dead on Saturday afternoon.
Detective Senior Sergeant Geoff Baber said the death was an "absolute tragedy" and a team of 20 investigators would work on the case.
"A scene examination has been conducted at an address in Auckland City and a post-mortem will be carried out," he said.
"We are continuing to speak with a number of people in relation to this investigation and have no further updates at this stage."
Oranga Tamariki is the government department responsible for the wellbeing of children, specifically those at risk of harm.
Based on her own experiences and "very personal opinion", Money said the agency was not fit for purpose and changes needed to be made.
"I don't think that the service is delivering everything that it needs to do to make sure the community or whānau flourish.
"When you take [children] out of a dangerous environment and allegedly put them in a safe environment, which is state care, they often come out worse than they started.
"I think the problem is bigger than all of these uplifts, absolutely we need to look at that, but we need to step back and look at humanity."
Last month Children's Commissioner Judge Andrew Becroft announced a review into Oranga Tamariki in relation to its uplift policies.