VANCOUVER -- Dozens of children die every year in the U.S. after being left in a hot car, most of them under the age of three. In Canada, the number is lower but the risk is the same.

Even on days with mild temperatures, the heat inside a vehicle can reach dangerous levels within an hour, posing significant health risks to small children and pets left inside. And the risk is ever-present. Earlier this year, a four-year-old boy in the U.S. died after sneaking out and into the family car unnoticed. 

"Because everyone's home more often than usual, parents need to make sure that their keys are always out of reach of little hands," says Emily Thomas with Consumer Reports. "And that their vehicles are locked at all times." 

The risk hot cars pose to children may be higher than usual this year. Because of the pandemic, most stores have implemented restrictions, limiting the number of people allowed inside at a time. Parents may be tempted 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 temperatures of the car can reach dangerous levels in a short period of time. 

"Children's bodies heat up three to five times faster than adults," Thomas says. "That's why it's never safe for them to be left unattended inside of a closed vehicle. 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 effects them differently and it's never safe." 

A study from GM found that on a 35 degree day, a small car in the sun could get hotter than 50 degrees in just 20 minutes, and up to 65 degrees in 40 minutes. And it found that leaving the window cracked didn't alleviate the heat. 

To keep your kids safe, leave them at home and arrange for childcare when running errands. You should also keep the car locked when it's in the driveway or in the garage, so kids can't get in when you're not looking. 

And make it a habit to keep your cellphone or purse in the backseat. That way, you'll have to turn around and check the backseat every time you get out of the car. 

If you spot a child or a pet that's been left in a hot vehicle, call 911 right away.  

With files from Consumer Reports