about the booster seat/car seat. I wouldn't dream of using just a seatbelt. Seatbelts are not designed to fit young ones properly. I read that most serious injuries to their abdomens are not from the crash itself, it's from the seatbelt "cutting" into their bellies causing internal injuries. They are much better off in a high back booster and strapping them in with the seatbelt until the appropriate size/weight.