The pills were believed to have been a "fat burner".
The kids, who were all assessed and "appeared well" after four hours under precautionary observation, are now being discharged.
They're being told to return to hospital if they develop any symptoms, but "we're not expecting any problems," the spokeswoman said
Principal Neil Baker breathed a sigh of relief at hearing the news. "It's been a really good learning curve from our point of view."
Mr Baker said the pupils had tried the pills on school grounds before classes started at 9am.
The 6-year-old girl had found the plain pills in an unlabelled, screw-lid container near the school grounds on Tuckers Rd, Redwood.
Once she arrived in the playground, she gave the container to her 8-year-old sister.
Twelve boys and girls, from two classrooms, swallowed the tablets - but some children spat them out, Mr Baker said.
A teacher "got wind of it" and asked what they had done.
"The child who found the pills gave them to somebody else who then decided to say, 'Ooh, let's try one', and obviously gave it around a number of children," he said.
"We just didn't know what they had taken.
"There's no label on the contents. It could be peppermint, it could be a herbal remedy, it could be I don't know what."
The alarm was raised and emergency services called shortly before 10am.
Three ambulances and two response vehicles were sent to the scene.
St John paramedics thought it could be a "mass poisoning" and took them all to hospital, with reports of some of them complaining of sore stomachs. None were in a serious condition, and they have been released and are in full health.
Mr Baker said the school secretary's phone had been "hot" trying to contact families of all of the school's 150 pupils.
A spokesman for Christchurch Police said they have concluded their assistance and enquiries at the school.
"We don't expect to have any ongoing involvement or investigation, other than liaison with the school over raising awareness among pupils about the dangers of taking unknown pills."
Mr Baker said the children would be spoken to, to find out out more about what happened.
He stressed they would not be punished, but a school assembly might be held to warn of the dangers in taking unknown pills.
"It's very hard to stop a child from putting something in their mouth," Mr Baker said.
"It's a real good learning curve again about children being careful with anything that looks like a pill. But the problem is that their sweets look like a pill.
"The message here is: 'If you don't know, don't take'."
