Using a safety seat correctly makes a big difference. A child safety seat may not protect your child in a crash if it isn't used correctly and installed in the vehicle properly.
Cars were made for adults, therefore children do not fit in a seatbelt properly until they are 4 feet 9 inches tall.
Compliments of Rasing Arizona Kids
Transcription available upon request
You can use an infant or convertible seat as long as the seat fits your child’s weight and height and fits in your vehicle. Children should ride rear facing in their car seat to the upper weight limit of the seat until 35 to 40 pounds in most cases with convertible seat and some with infant seats. A rear facing car seat absorbs the force of a car crash, so do not turn the seat around before they mean the weight limit. They cannot be turned around before the child is one year old and weighs 20 pounds.
Children should ride rear facing until they are 1 year old or weigh 20 pounds; it is recommended they ride rear facing until they are 2 years old or outgrow the weight limit on their seat.
Harness seat weight limits vary depending on the seat. Common weight limits are 40, 65, and 80 pounds. Harness straps should be at or above the child's shoulders.
Children should stay in a full harness until they have out grown of it. All harnesses fit children up to 40 pounds and most are now increasing that to 65 pounds or higher. The longer your child is in a full harness the safer they are. When children outgrow their car seat they should ride in a belt-positioning booster seat in the back seat. The booster seat uses the adult lap and shoulder belt and should be used until the belt fits the child properly or until they are at least 4 feet 9 inches tall.
If there is a "no" answer to any of these questions, the child needs a booster.
If all the answers to the five-step test (above) are “yes” then the child can sit in both lap and shoulder belts. The shoulder belt should be snug against the child's chest, crossing at the collarbone. The lap belt should lay low across the child's upper thighs. Never allow the child to put the shoulder belt behind his back or under his arm. Remember, kids are not allowed in the front seat until they are 13, as airbags can cause death or serious injuries.