Atkinson is an English-language surname. The name is derived from a patronymic form of the Middle English Atkin.
These are much more conservative than state laws, in general (for instance, everyone should be in a booster seat from about age 4 to at least age 8) but remain less conservative than some of the european standards (for instance, the European Child Safety Alliance recommends that children remain in rear-facing carseats until 3 years of age).
Keep children in each seat up to the maximum age/weight/height limits before moving to the next phase. ALL children younger than age 13 years should ride properly restrained in the back seat. But until they reach phase 4, they need to be strapped in properly in a safe car seat.