What component is involved in locking the belt for the child restraint system in vehicles?

The sliding latch plate is essential for locking the seatbelt in a child restraint system. When the seatbelt is threaded through or around the child restraint and the sliding latch plate is moved, it effectively locks the seatbelt, securing the child restraint in place. This mechanism prevents the seatbelt from retracting or loosening, ensuring that the child restraint maintains a tight fit against the vehicle seat.

Other components mentioned in the options serve different functions. The detachable base is used with some types of child restraints to facilitate easy installation and removal but does not lock the belt itself. The positioning booster is designed to correctly position a child's body so that the vehicle's seatbelt fits properly, rather than locking it in place. The shoulder pad is a comfort feature that can provide cushioning but has no role in securing or locking the seatbelt. Understanding the function of each component is crucial for ensuring the safety of child passengers in vehicles.