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).
Once your child outgrows their car seat, they'll need to switch to an appropriately sized booster seat. It's recommended that your child remain in a booster seat until they're at least 57 inches, usually between the ages of 8 and 12.