With temperatures expected to stay in the 90s for most of the week, Knoxville Police are warning parents not to leave children and pets in hot cars.

So far this year, 13 children nationwide have died from heatstroke after being left in a car. 10News placed a thermometer inside a car when the outside temperature was 85 degrees. After 30 minutes, the thermometer read 104 degrees.

Research shows the temperature can increase 10 degrees in just 20 minutes.

"What people really don't realize is just how quickly a car can warm up inside," said Knoxville Police Spokesperson Darrell DeBusk. "A child's body reacts differently to heat than an adult body. They shut down. It can create, if it doesn't kill them, long-term health issues."

The dangers triggered new legislation in Tennessee this year to protect those trying to help.

Rep. David Hawk (R-Greeneville) sponsored a bill that allows you to break into a car to get a trapped child out. The legislature passed the bill and it goes into effect next week.

Knoxville Police say every summer they get calls about a child being left inside a hot car.

Through 2012, Tennessee ranked fourth in the nation for child deaths in hot cars.

"Only California, Texas, and Arizona had more child deaths behind Tennessee. That's very disturbing," said DeBusk.

The stories of those children inspired Hawk to write a bill to protect people trying to help trapped kids.

"This will go a long way to saving a child," Rep. Hawk said.

The good samaritan law allows you to break into a hot car if you see a child without an adult. The doors must be locked and the child must be in danger.

"There's a couple of things they have to do before they just automatically break out the window. First and foremost they have to call 911. They have to alert the authorities," DeBusk said.

After you call 911, the law requires that you stay with the child until law enforcement arrives.

"No other state has any other legislation similar to this. This is some groundbreaking good samaritan legislation," Rep. Hawk said.

Knoxville Police praise the law but hope it never has to be put to use.

Instead, they urge all parents never leave your child or your pets in a hot car.

Police say cracking a window doesn't help the temperature.

KPD suggests creating reminders so you never leave your child in the first place, such as leaving your diaper bag up front or your cell phone and purse in the back seat.

The bill goes into effect July 1st.