Arizona law requires all children under the age of five must be seated in a legally recognized child restraint system. The Arizona booster seat law demands that any child under eight years of age and shorter than 4'9′′ are secured in a child restraint system.Arizona law mandates that children under the age of eight and shorter than 4 feet 9 inches must be secured in an appropriate child restraint system. In Arizona, children need to sit in some sort of child safety seat until they are at least 4 ft and 9 inches and reach the age of eight. The state of Arizona requires that all children who are younger than eight years old and under 4'9" are properly secured in a child safety seat. For children under a year old, Arizona law requires a rearfacing car seat that supports the entire body, including the head and neck areas. Arizona Laws for Child Safety Seats. All children under five years old must ride in child safety seats while in motor vehicles. ARIZONA CHILD BOOSTER SEAT LAWS​​ In Arizona, any child between the ages of five and seven is required to sit in a booster seat. A (child restraint law) and ARS §28-907.