TORONTO -- As a heat warning goes into effect across southern Ontario, parents are reminded to be careful of young children in hot cars.

A study by The Hospital for Sick Children found that even with an outside temperature of 22 C a car's interior temperature can rise above 40 C in just one hour.

“Even if you're not in your car and the car is in your driveway, don't leave the doors unlocked as children can climb in on their own" Pamela Fuselli with the safety group Parachute Canada said.

Last year, 53 children died in hot cars in the United States. This year, seven children have died, including Ryan and Teagan Dennis of Tulsa, Okla. Last month, the children, aged three and four, climbed into their father's truck, shut the doors and never got out.

The Hospital for Sick Children said that on average a child dies in Canada each year after being left in a hot car.

Due to the COVID-19 pandemic, health officials said the number could be even higher this year as more people have their vehicles at home or may decide to leave their children in a car when they go shopping.

Restrictions at stores could tempt some parents to leave their child in the car to decrease the risk of exposure to COVID-19 while they shop, but even with the window cracked or the vehicle parked in the shade, the interior temperature can become extremely hot in a short period of time.

“Children's bodies heat up three to five times faster than adults. That's why it’s never safe for them to be left unattended inside of a closed vehicle,” Emily Thomas with Consumer Reports said.

“It doesn't matter if you're parked in the shade, or if you've left the window cracked, or even if you think it’s not that hot out. It affects them differently and it’s never safe.”

Some vehicle manufacturers have created rear occupant alert systems that can sense the movement of a child in a car. An alarm will sound and a message will be sent your phone.

The Toronto Humane Society also released a public service announcement reminding pet owners to “look before they lock” to make sure pets aren't accidentally left in a hot car.

Parents are advised to get in the habit of checking the back seat before locking their car doors. Another strategy is putting your cell phone in the back whenever a child is there so you'll see them when you go to retrieve your phone.