The minimum height for a backless booster seat is 4 feet, 9 inches. This height requirement is based on the fact that most children will not be tall enough to safely fit in a vehicle's adult seat belt system until they are at least this tall. A backless booster seat helps raise your child up so that the shoulder strap of an adult seat belt fits properly across their shoulder and chest rather than their neck or face. Keeping them safe and secure during every car ride should always be your top priority, and making sure they are using the correct type of safety seating is essential for keeping them safe while on the road.