Florida law allows a child to start using a booster seat at age four. Florida law states that children ages 4 through 5 must be in a separate carrier, integrated child seat, or booster seat.Florida state legislators voted to support a new bill that would make it booster-seat use mandatory for children from the ages of 4 to 7. Florida law requires parents and guardians to ensure their children sit in age and sizeappropriate car or booster seats. Like the other types of car seats, Florida law does not recommend the weight or height at which your child should switch to a booster seat. 1. For children aged through 3 years, such restraint device must be a separate carrier or a vehicle manufacturer's integrated child seat. Car seats for kids under 5 and under 40 pounds are required if the vehicle has seat belts. The parent is responsible for ensuring the children are in car seats. Florida car seat laws require children up to age 5 to be secured in a crash-tested, federally approved child restraint device. Children aged 45 must use a separate carrier, an integrated child seat, or a booster seat.