Surveillance footage shows the children, including a 5-month-old baby, were left in the van in the casino complex car park for about 45 minutes from 11am on Sunday, February 26.
Security guards worked with police to free them after a couple found them trapped and crying.
The Green Party has said the case highlighted the impact of problem gambling, which would escalate ahead of its plan to let SkyCity operate more pokie machines.
Prime Minister John Key defended the SkyCity development in the wake of the incident, saying it could equally have happened at an environment like a supermarket.