It is best to keep kids in the foreward facing car seat for as long as they fit comfortably in it. Older kids over 40 pounds should ride in a booster seat until the car's lap and shoulder belts fit right. The lap belt must fit low and snug on their hips. The shoulder belt must not cross their face or neck. Never put the shoulder belt behind their back or under their arm.
All kids are safest in the back seat, in a safety seat or seat belt.
Always read the child seat instructions and the car owner's manual. Test the child seat to ensure a snug fit by pulling the base to either side or toward the front of the car.