Two early childhood teachers have been suspended after walking seven toddlers through a Wellington tunnel as traffic passed at 100km/h.

The group were walking hand-in-hand through The Terrace motorway tunnel on a narrow concrete ledge and were 100m into the 435m-long tunnel when police saw them. The teachers have also been fined $250 for walking on a motorway and are facing disciplinary action, including dismissal.

At least one parent is believed to have pulled a child from the Early Years Childcare Learning Centre in Leeds St. The company runs two other centres in Wellington and has suspended all outings while staff review policies relating to taking children on outings, said operations manager Fiona Hughes.

The teachers had breached centre policy on child safety and also early childhood regulations, she said.

They would meet their employers today to explain their actions.

One is a qualified early childhood teacher and the other is training for her qualification.

"There is a policy in place that would never allow a situation like that to occur, and they've made a very poor judgment on the spur of the moment," Mrs Hughes said. The children, aged between 3 and 5, had been on a short walk which was approved by parents when they enrolled in the childcare centres.

Police said they received a number of calls from concerned motorists about the group. One teacher was leading a group of three youngsters and the other adult was supervising four.

Senior Sergeant Richard Hocken said a patrol car had to make a dangerous u-turn in the tunnel and other vehicles overtook it at speed into oncoming traffic. A second police car was called to remove the teachers and children and take them back to the childcare centre.

"We thought the kids would have been petrified," Mr Hocken said.

"I'm aware of one of them who was fairly outgoing who was thoroughly enjoying it and thought the final buzz was getting a ride in the police car.

"So one hopes they're not traumatised by it - but it could have been so much different. If one of them had slipped there wouldn't have been a chance.

"It appears there has been an ad-hoc, off-the-cuff decision to ... go through the motorway tunnel to get to a grassed area at the north side.

"How these two adults managed to come up with such an idea without thinking about the consequences beggars thinking about."

Mr Hocken said the children's parents were contacted and the police also wrote to the families about the decision to fine the teachers.

Officers had considered charging them under the Crimes Act with endangering public safety.

He said police issued tickets to people who walked through the tunnel "from time to time".

"This is the first time we've ever had something like this and I hope it's the last."