Dr. Michael Smith: If you've ever been tempted to leave the kids in the car while you run a quick errand, listen to this: At least 17 children -- and sadly, that number is likely to rise, have died from heatstroke this year after being left alone in cars. It doesn't have to be a hot day to be dangerous: Experts showed that in sunny 72 degree weather, a car's interior can reach 117 degrees within an hour. In states with milder winter temperatures, the danger is there all year round. Most of the heating happens in the first 30 minutes. Leaving the windows cracked or having the A/C on before you turn the car off doesn't help. Infants and young children are more vulnerable to heat than adults, so bad things can happen quickly, including brain damage and death. So don't even think about leaving kids or pets in your car unattended -- it's simply not safe. For WebMD, I'm Dr. Michael Smith.