A child safety seat includes a seat shell for receiving a child, an extension member, an extension locking mechanism operable to lock the extension member with respect to the seat shell, and an anti-rebound part. The anti-rebound part can be installed on the extension member or the seat shell. The child safety seat is installable on a vehicle seat in a rear facing position with the anti-rebound part extending at an angle above the extension member and adjacent to a seatback of the vehicle seat.