A lateral protecting mechanism adapted for a child carrier is provided and includes a protecting block, a locking component, a driving component and an operating component. The protecting block is pivotally disposed a lateral portion of the child carrier. The locking component is slidably disposed on the lateral portion of the child carrier and configured to slide to abut against the protecting block for restraining a pivoting movement of the protecting block. The driving component is located at a position corresponding to the locking component for driving the locking component to slide to abut against the protecting block for restraining the pivoting movement of the protecting block. The operating component is coupled to the driving component for driving the driving component to pivot to drive the locking component to abut against the protecting block when the operating component is operated. Besides, a related child restraint system is provided.