"We are extremely remorseful and we implemented immediate procedural changes to ensure that this never happens again.''
The company is set to reappear on the charge, laid by the Ministry of Business, Innovation and Employment, on July 1.
The incident happened during a gathering of ASB Bank staff at the Whangarei park for an annual children's Christmas party.
Northland St John Ambulance boss Tony Devanney said a wind gust was believed to have picked up the slide and dragged it about 20 metres. Three children were on it and the equipment was believed to have hit another child as it was blown along.
Four children were taken to hospital, Mr Devanney said.
It was understood twin 6-year-old boys suffered broken arms and an 8-year-old girl was concussed.
ASB Bank general manager of public and external relations Christian May said at the time a strong gust appeared to have pulled the slide's tethers from the ground and tipped it over.