Many parents are allowing their children to use a seat belt alone before they are big enough, according to a new study by Safe Kids Worldwide as part of National Child Passenger Safety Week. 

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The study found that nine out of 10 parents move a child from a booster seat to a seat belt too soon, and seven out of 10 parents don't know that a child should be at least 57 inches to ride in a car without a booster seat.

Aside from getting out the tape measure and measuring a child's height, there is a visual test that parents can use to see if their child is, in fact, tall enough to leave the booster seat.

"You want to make sure the child's back and bottom is against the back and seat of the car, and you want to make sure that their knees bend at the edge of the car seat," said Kate Carr, president and CEO of Safe Kids Worldwide. "You want the seat belt to sit across their upper thighs near the hip bones rather than the abdomen and for the shoulder belt to ride across their shoulder and chest, not their neck or face. When the belt is against the abdomen or neck and face, if there is a crash, the child can suffer injuries that can be avoided if the child is in the appropriate seat."

The study found some parents are engaging in risky behavior when it comes to their child's safety with one in four parents reporting they don't buckle up their children on every ride.   One in five parents whose children carpool say they "bend the rules" when driving, letting children ride without seatbelts or the car seat or booster they would normally use.

National Child Passenger Safety Week runs until Sept. 20, culminating with National Seat Check on Saturday during which Safe Kids Worldwide will host more than 500 child seat inspections across the country. Certified child passenger safety technicians will be on hand to offer tips on proper installation of child safety and booster seats.

To check that a car seat is installed properly, parents can find a checklist here. To find tips on car seat safety, click here.