At age 3 your child grows quickly and starts interacting with you at a level that makes you think that they are ready to get rid of the big, forward-facing car seat and start using a booster seat. However, the NHTSA recommends that the earliest age that a child uses a booster seat is age 4. Remember that you should only allow your child to move to the next level of car seat if they meet the age requirement as well as the height and weight requirements according to the manufacturer’s guidelines.