An autopsy has confirmed that a two-year-old boy died of heat exposure after being left alone in a hot car in Milton, Ont. for an “extended period of time,” according to police.

Halton police said the toddler was found around 5:30 p.m. on Wednesday after being left in a small sedan. At the time of his death, the young boy was in the care of his grandmother because his dad was at work and his mom was at an appointment, police said in a news release Thursday.

The victim's five-year-old sister was in school at the time and remains in the care of her parents, police said.

The car, parked just outside of the garage of a home in a residential area, was towed away late Wednesday by police.

Neighbours left flowers on the doorstep of the home Thursday, as some expressed shock and grief over the tragedy.

Detectives from the homicide unit are canvassing the area and conducting interviews to determine the exact sequence of events. The investigation is ongoing.

No criminal charges have been laid.

Temperatures in Milton exceeded 30 C with high humidity on Wednesday as southern Ontario was under an extreme heat alert.

According to police, research shows that a vehicle’s interior heats up very quickly with the majority of the temperature increase taking place in the first 15 to 30 minutes.

Pediatrician Dr. Sean Godfrey told CTV News he sees dozens of children suffering from heat stress every summer.

Babies and toddlers are much more susceptible than adults, and may suffer permanent damage after being trapped in a car in less than 15 minutes.

“They’ll very quickly decompensate, they’ll hyperventilate, may have seizures, and then become comatose and unfortunately succumb,” Godfrey said.

Alarmingly, similar incidents of child entrapment in hot vehicles are on the rise.

Northwest of Milton, in Markham, Ont., a woman was charged Thursday with child abandonment after her two-year-old daughter was left in a sweltering vehicle.

After a call was placed to 911, police forced a window open and rescued the child. The mother was arrested when she returned to the car from shopping, police say.

In the U.S., 15 children have died this year in closed vehicles, prompting some companies to start selling car-seat alarms to remind parents to turn around. But the department of transportation says the alarms are unreliable and may dangerously change the position of the child in the seat.

With files from CTV’s Peter Akman