what weight do you need a booster seat
Stephanie Tombrello. child passenger safety specialist. You can safely switch your child to a booster seat if she's at least 4 years old and she weighs 40 pounds or more or has grown too tall for her car seat (when her shoulders are higher than the top set of harness-strap slots in the car seat's back).n a crash, belt-positioning seats are far safer. (If you have only lap belts in the rear of your car, select a booster seat with an extra energy absorber belt.) Backless booster seats tend to provide a better fit than the high-back kind, and are more portable when you're switching them from car to car.