All 50 states and the District of Columbia have some law regarding child safety seats.
In Maryland, children under 5 or less than 40 pounds must be in a child restraint. Children over 40 pounds or between the ages of 6 and 15 must wear a regular seatbelt.
Virginia is similar; however, the state leaves out the weight restriction. Virginia requires children under 5 to be in safety seats and children between 5 and 16 to wear seatbelts.
The District of Columbia requires children under 7 to be in safety restraints and children between 8 and 15 to wear seatbelts.
Sources: Insurance Institute for Highway Safety Seatbelt Laws Insurance Institute for Highway Safety Child Restraint Laws