The children were rushed to hospital for treatment along with the driver of the car, an 80-year-old woman who suffered shock and minor injuries to her back, said Const. Franco Di Genova.
The three girls were aged three, four and five years old and were not seriously injured, Di Genova said, adding one of them had been released from hospital and another was expected to be sent home by the end of the afternoon.
One little girl was either hit by the vehicle or flying debris and suffered wounds to her face, said Di Genova. She was expected to be released from hospital on Wednesday.
A doctor at Montreal's Ste-Justine Hospital said she is stable and that the injuries could have been much worse.
"We're pleased the injuries are not as serious as we could imagine given the situation," said Dr. Antonio D'Angelo, the emergency room chief at the hospital.
The daycare is located at street level in a strip mall on one of the main streets in the city north of Montreal.
About 30 uninjured children were gathered by daycare workers after the crash and walked to another nearby daycare centre to wait for their parents to pick them up.
Shaken parents arrived shortly and bundled their children out of the area.
"Most of them didn't see much because it was during their nap time," said a man who identified himself as Dominic.
"It's pretty shocking, it's sad," he said as he clutched his three-year-old girl close. The little girl, who has attended the daycare since September, was not injured.
"She was very lucky," her father said.
He said daycare workers were doing their best to cope.
"They're in shock. It happened so fast."
Di Genova said calls started to come in to the 9-1-1 emergency line immediately after the crash around 2 p.m.
"We didn't take any chances," he said. "Every available unit was sent."
Di Genova said police plan to meet with the driver as they try to determine the cause of the crash. He said the car was in the parking lot before the incident.
"Did the woman have some kind of medical situation just before or did she have it in drive when she thought it was in reverse," he said. "We've seen that in the past also.
"But it took quite a bit to go through the plate glass window. As you can see, there's a sidewalk, there's a little bit of a border before you go through the window."
Colourful comic book characters looked down from the brightly painted walls of the room as police combed the scene around the silver Ford Focus, which took out the entire front window of the Face-a-Face daycare when it hurtled into the building.