Once a child weighs more than 40 pounds, the next step is a belt-positioning booster. While Maine law requires kids to be in a car seat until age four, Gilpatrick recommends that you keep you're child in one much longer. Some car seats aren't compatible with certain vehicles or can't be used safely in certain positions. Before you buy the seat, most places allow you to take the store model outside to your car. In order for it to fit properly, the base of the seat should not be wider than the anchor points of the seat belts.
All kids are safest in the back seat.
Carefully read both the car seat instructions and the safety seat section of your vehicle owner's manual. Throw a car seat away after six years because the integrity of the plastic decreases. Discard the seat if it's been in an accident. Have the seat inspected by a certified child safety seat technician in your community. You have to be willing to go home if they're not willing to follow the rules.