A group of four children were hit by the truck at Cliffside Drive and East Haven Drive, which is close to the intersection of Midland Avenue and Kingston Road.
Two other children — a six-year-old boy and a 13-year-old girl —were taken to hospital with minor injuries.
The fourth child was not injured, police said.
The accident happened at about 3:45 p.m. as the children were heading home from Cliffside Public School.
Details of exactly what led to the accident remain unclear.
All police will say is that the 62-year-old driver was collecting garbage at the time and making a left-hand turn when the children were crossing the street.
Paramedics rushed the children to hospital, but police later confirmed the five-year-old had died.
One person at the scene of the accident told CBC's Charlsie Agro that the five-year-old was named Kaylie.
"That same person says that Kaylie is one of four children and that, remarkably, her mother is apparently in hospital right now, potentially giving birth to another child," she said.
A witness told CBC News he saw the garbage truck peel around a corner.
"The truck apparently turned the corner and that's when the young girl was hit," Agro reported.
Toronto Mayor Rob Ford released a statement promising the city would co-operate with any investigation.
"I was shocked and deeply saddened to learn that three children were struck, one fatally, by a city garbage truck. It’s with a heavy heart that I extend my deepest condolences to the victims during this difficult time … We will do everything we can to assist the families. The city will co-operate fully with the investigation," the statement said.
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