Tom C
maybe not a car seat at those ages but certainly a booster seat at the very least

Kak22
A lot of states require children to be in a booster until at least age 8, but children should really ride in boosters until the adult seatbelt fits them and they pass the 5 step test (usually around age 12).

4kkz
deff in a booster seat until 80lbs. find out about a local car seat safety check in your area..it is free and may save their lives. Just b/c overweight, doesn't mean they are tall enough to be in adult seat, nor their organs can be protected as well.

UCANTCME
Try this site.....................

littleangelfire81
Kids need to be in a booster seat until: -They are both 4'9" tall AND 80lbs -They are 8-10 years old AND they pass this 5 step test: 1. Does the child sit all the way back against the auto seat? 2. Do the child's knees bend comfortably at the edge of the auto seat? 3. Does the belt cross the shoulder between the neck and arm? 4. Is the lap belt as low as possible, touching the thighs? 5. Can the child stay seated like this for the whole trip? And most states now have a law requiring boosters seats for kids until they are 6-8 years old and/or 60-80lbs. And, by the way, 60-70lbs 6,7, and 8 year olds are not necessarily fat at all. That's the average weight for those age children.