All three have been cleared and discharged from hospital.
She was called by teachers on the bus after the incident and parents were sent texts and emails informing them of the crash.
The children were "a bit shaken up" but were all okay, she said. "It was just that sudden stop, jarring, and the shock of the whole thing."
"At the end of the day it's one of those things that happen. We're lucky there were no serious injuries."
The Ritchies buses were hired for the day.
Ritchies has not been in contact with the school as it was outside office hours but they would likely speak in the morning, Stavert said.
Glen Eden often used Ritchies buses for trips, she said. "We haven't had any issues in the past - it's pretty unusual."
The Ministry of Education's traumatic incident team would be at the school in the morning, she said.
Ritchies transport director Andrew Ritchie said the company was investigating the crash.
The crash came just before he appeared on Newshub this evening speaking about a mass shortage of bus drivers in New Zealand.
Ritchie is having to drive some buses himself when no drivers can be found.
The crash happened on the westbound side of the motorway, after the St Lukes offramp, according to the NZ Transport Agency. Police said the crash happened on the Great North Rd offramp.
It was cleared from the lanes but "rubberneckers" caused delays after the crash, with traffic heavy from Grafton Gully to Great North Rd during peak commute time.
