S.C. Code Ann. § 56-5-6410
Every driver of a motor vehicle (passenger car, pickup truck, van, or recreational vehicle) registered in this State or primarily operated on the highways and streets of this State when transporting a child under six years of age upon the public streets and highways of the State shall provide an appropriate child passenger restraint system and shall secure the child as follows:
(2) Any child four or five years of age must be secured by a safety belt provided in the motor vehicle unless properly secured in a child restraint system which meets the standards prescribed by the National Highway Traffic Safety Administration.
Any child restraint system of a type sufficient to meet the physical standards prescribed by the National Highway Traffic Safety Administration at the time of its manufacture is sufficient to meet the requirements of this article.