A: Always check your own car seat and its instructions but, in general, 20 lbs. or 28 inches are the weight and height maximums for an infant seat. "Convertible" car seats are the next step up, but a younger child should sit rearfacing until age 2. Kids older than 2 can have car seats that are forward facing until they are ready for a booster seat. Some car seats be used for quite a while--like several years--so they are a good investment.