The students were being treated at Children's Hospital in Calgary. The female bus driver was in serious condition in another hospital.
Deputy Fire Chief Judy Unsworth with Rocky View County said the accident happened about 8 a.m. near Crossfield. She said the children were treated by paramedics and firefighters on the scene before being sent to hospital.
"They were all very brave and ... my heart goes out to them. They were trying not to cry and (were) very shook by what was happening," Unsworth said.
Information provided by police and health officials about the number of children hurt in the crash changed throughout the day.
A Rocky View Schools official said there were four other students on the bus who were not injured.
Some motorists quickly stopped to help the children get off the bus.
"There was some sort of medically trained person with the military and a number of good Samaritans and eyewitnesses provided some aid so it was nice to see," said Adam Loria from Calgary EMS.
"For everybody involved today it was very scary, especially when you see a school bus involved and children hurt."
RCMP Sgt. Glen Demmon said it's always difficult when an accident involves children.
"There was a little bit of shock at first. I have children myself, but coming across the scene, the bystanders were really good. They had the scene contained and controlled," he said.
"They were looking after the victims and they were here on scene prior to EMS and fire department and seemed to have it well in hand."
The yellow bus was upright against a guardrail and a large pickup truck with "JMS Mechanical Services from Calgary" written on the side was nose down in a ravine after smashing through a reinforced guardrail.
The front end of the bus was crushed and missing its windshield. Glass and auto parts were scattered across the road.
RCMP Const. Robert Frizzell said the truck was a one-tonne Ford F-350.
Crossfield Mayor Nathan Anderson said the children attend Crossfield Elementary School, one of two schools in the community of 3,000. There were also a few students on board from W.G. Murdoch School. The children ranged in age from 5 to 13.
"I am very concerned. Our prayers go out to those kids and families," Anderson said. "We just hope, God willing, they are all OK and will pull out of this without any lasting effects."
Frizzell said it's not yet known what caused the crash.
"We're not quite sure what the contributing factor to this collision was, whether that's limited visibility or road conditions or what's actually there," he said.
"We've contacted our collision reconstructionists out of Calgary to attend and determine that."
The school division immediately sent crisis counsellors to the schools in Crossfield.
"My heart goes out to the students and parents directly impacted by this incident. We are very concerned about the well-being of our school communities," said Susan William, acting superintendent of the Rocky View School Division.
William also sent a letter to parents advising them how to talk to their children about what happened to their classmates.
The letter suggests they try to speak to their kids about how they feel.
"Please be assured, our teachers and staff will be taking extra care in the coming days to observe students who may be exhibiting signs of stress as a result of this accident," the letter reads.
"Parents wanting more information on how to help their child deal with the accident and any stress their child may be experiencing should contact your child's teacher."
Alberta's education minister also expressed concern.
"I understand that a number of children and the bus driver have been transported to medical facilities, where I know they will get the best level of care possible," said Jeff Johnson.
“My thoughts and prayers are with the families and school communities of all those involved in these unfortunate incidents."
— With files from John Cotter in Edmonton
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