Did anybody send their Aunt Betty to look at the Car Seat stuff? If so, she left you a comment on the "laws" post. :) Tee hee!
To follow up on that, I have found out that several states now require that a child be in a booster until 8 years old and 80lbs. The laws really are the bare minimum and are slow to catch up to research. Also, that car manufacturers make seat belts to fit people 4'9" or bigger. If your kiddo is shorter than that, they are smaller than the person seat belt was made for.
ETA: I'll just post some of the surrounding states:
Arkansas, as I said, must be in some sort of restraint until 6 years AND 60lbs (must meet both).
Tennessee- younger than 1 year or 20 pounds or less in a rear-facing infant seat; 1 through 3 years and 20+ pounds in a forward-facing infant seat [remember that RFing is 4 times safer than FF! Keep those babies RFing!!] ; 4 through 8 years and less than 4'9" in a booster seat. Also, children 8 years and younger and less than 4'9" must be in rear seat if available; rear seat recommended for children 9 through 12.
Missouri- 3 years and younger must be in a child restraint; all children who weigh less than 40 pounds must be in a CR; 4 through 7 years who weigh at least 40 pounds but less than 80 pounds and who are 4'9" or shorter must be in either a CR or booster seat; children 4 years and older who weigh at least 80 pounds or who are at least 4'9" tall must be in either a booster seat or safety belt.
Mississippi-3 years and younger must be in a child restraint; 4 through 6 years and either less than 57 inches or less than 65 pounds must be in a booster seat
Texas-4 years and younger and less than 36 inches [Shame on Texas!]
Oklahoma-5 years and younger [Shame on Oklahoma, too!]