Arkansas does not specifically say that children under 1 year must be RF, but that children under 6 and less than 60 pounds must be in a proper child restraint (this is called a "proper restraint" law) . But since there are not any seats that allow children under 1 year to be FF, the "proper restraint" for a less than 1 year old is a RF seat and putting them FF would go against that part of the law.
Re: QUICK! Car Seat laws in Arkansas