Booster Car Seat Basics Share this article Print article Wondering what the main parts of a booster seat are, and what they do for your child? Check out this “Booster Car Seat Basics” guide! Headrest Provides support for the back and sides of the head. Also provides a place for sleeping children to rest their head safely while remaining in the proper position. Shoulder belt guide Helps to position the shoulder belt properly across the child’s upper torso. Bottom of belt guides should be at or above child’s shoulders. Seat back Helps to keep child sitting upright and in the proper position for optimal seat belt placement. Lap belt guide Helps to position the lap belt low across the child’s hips.