PHOENIX -- Car crashes are the No. 1 killer of children in Arizona, yet the number of parents refusing to put their children in car seats has increased 2 percent since 2008, according to a study from the National Highway Safety Administration.

Additionally, four out of every five car seats nationwide are improperly installed, the study found.

It's against the law for any child under 5 years old to ride in a car without a child safety seat.

Phoenix police Officer Steve Petrey told 5 Investigates he could write a half-dozen citations each shift for safety seat violations.

"The odds are definitely against (children) if they are not in a seat," Petrey said.

When confronted about their children not using a car seat during one of Petrey's shifts, adults gave excuses ranging from "she got out of (the seat)" to "this car is so small it's hard for me to even put the car seat in."

Even if the child is buckled in, during a recent safety expo, 5 Investigates discovered 95 percent of parents did not install the car seat properly.

"I had one of them in correctly. The other was not -- the seat belt was kind of wrong," mother Davianne Fife explained at the expo. "It was a little scary because if we got into a car crash, we don’t know what would have happened because it was wrong."

Children must be at least 1 year old or weigh 20 pounds to ride facing forward, and the seat's harness should be snug over the child's shoulders.

More information:

• Read: Car Seat Safety Tips