The parents, who were known to Child, Youth and Family, left five children locked in a van on Sunday while they gambled at SkyCity Auckland.
Surveillance footage shows the children, including a 5-month-old baby, were left unsupervised in the van for about 45 minutes from 11am on Sunday.
The oldest child was aged eight.
The case highlighted the impact of problem gambling, which would escalate if the Government goes ahead with its plan to let Sky City operate more pokie machines, said Green Party gambling spokeswoman Denise Roche.
"The reality is, the more pokies there are, the more problem gambling there will be,'' said Ms Roche.
"The last thing we need right now are more pokie machines to add further fuel to these awful situations.''
The Government is understood to be changing regulations to allow the casino to have more pokie machines and gambling tables in exchange for it building a $350 million conference centre, said the Green Party.
On Sunday, security guards worked with police to free the children after a couple found them trapped and crying.
Their parents were found inside the casino using electronic gaming machines.
Child, Youth and Family northern region director Grant Bennett said there were concerns about the children's wellbeing before the SkyCity incident.
"We were already working with this family and had an agreed plan in place to address concerns these children may be at risk.
"This distressing and unacceptable event shows these parents have failed to stick to agreements they have made to ensure their children are safe.''
All five children had been placed with caregivers and were safe and well, Mr Bennett said.
"It is too early to say what the long-term care plans for these children will involve.''
Auckland police spokeswoman Noreen Hegarty said an investigation had been launched into the parents' actions.
A decision on possible charges will be made in the next few days, she said.
"It's on the face of it fairly reprehensible behaviour.''
SkyCity general counsel Peter Treacy said the incident was the worst of its kind in the 16 years SkyCity Auckland had been operating.
He thanked the couple who raised the alarm.
"This incident was extremely distressing for everyone concerned - the children, the couple who discovered them, our staff and police.''
Children had been found in cars at SkyCity seven times in the last year, Mr Treacy said.
SkyCity procedure was to call police immediately, advise the Department of Internal Affairs and issue a parent or guardian with a trespass notice when children were found, he said.