A child safety seat includes a seat shell having a seat region for receiving a child, two extension parts and a locking mechanism. The two extension parts are respectively disposed at a left and a right side of the seat region, are connected with the seat shell, and are coupled to each other via a linking assembly. The two extension parts are movable together relative to the seat shell to protrude forward from a front of the seat shell or retract toward the seat shell, the two extension parts being disconnected from each other at the front of the seat shell. The locking mechanism is operable to lock the two extension parts in position relative to the seat shell.