Remember that older kids should usually be in a booster seat until they are about 4-feet 9-inches tall and weigh about 80 pounds, when a car's regular seat belts will usually fit them well.
Signs that seat belts fit your child include that the shoulder belt fits across your child's shoulder, and does not go on his neck and you don't have to put it behind him. Also, the lap belt should fit low on his hips and not on his abdomen.
If your child is over 40 pounds, a booster seat would be a good idea until he really is ready for regular seat belts.
