A child safety seat (100, 100') comprising: a base for providing support on a vehicle seat and having a lengthwise direction extending from a rear end of the base to a front end of the base; a child support assembly coupled with the base, the child support assembly including a seat portion and a backrest portion, the backrest portion being pivotally connected with the base via a first pivot connection, the backrest portion and the seat portion being pivotally connected with each other via a second pivot connection located forward relative to the first pivot connection (Pl), the child support assembly being adjustable relative to the base between a sitting position and a recumbent position; a latch operable to lock the child support assembly with the base in the sitting position or the recumbent position, the latch sliding transversally relative to the child support assembly at one of a left and a right side thereof for engaging or disengaging the base; an actuator operatively connected with the latch, the actuator being operable to cause the latch to unlock for adjustment of the child support assembly between the sitting position and the recumbent position; wherein the latch and the actuator are coupled with the child support assembly, the base has a sidewall provided with a first opening and a second opening respectively associated with the recumbent position and the sitting position; and wherein the first opening is located above the second opening, the latch engaging with the first opening for locking the child support assembly in the recumbent position and with the second opening for locking the child support assembly in the sitting position, and the latch disengaging from the base for adjustment of the child support assembly between the sitting position and the recumbent position; characterized in that the actuator is pivotally connected with the backrest portion and is operatively connected with the latch via a linkage and a resilient arm, the actuator being affixed with a pin that is pivotally assembled through and is slidable along a guide slot which extends at an angle relative to a sliding axis of the linkage and is provided at an upper end of the linkage, a lower end of the linkage being connected with the resilient arm, and the resilient arm bending toward a left or a right side of the child support assembly where is disposed the latch, wherein the actuator is operable to cause upward sliding of the linkage and the resilient arm, which drives the latch to disengage from the base. a base for providing support on a vehicle seat and having a lengthwise direction extending from a rear end of the base to a front end of the base; a child support assembly coupled with the base, the child support assembly including a seat portion and a backrest portion, the backrest portion being pivotally connected with the base via a first pivot connection, the backrest portion and the seat portion being pivotally connected with each other via a second pivot connection located forward relative to the first pivot connection (Pl), the child support assembly being adjustable relative to the base between a sitting position and a recumbent position; a latch operable to lock the child support assembly with the base in the sitting position or the recumbent position, the latch sliding transversally relative to the child support assembly at one of a left and a right side thereof for engaging or disengaging the base; an actuator operatively connected with the latch, the actuator being operable to cause the latch to unlock for adjustment of the child support assembly between the sitting position and the recumbent position; wherein the latch and the actuator are coupled with the child support assembly, the base has a sidewall provided with a first opening and a second opening respectively associated with the recumbent position and the sitting position; and wherein the first opening is located above the second opening, the latch engaging with the first opening for locking the child support assembly in the recumbent position and with the second opening for locking the child support assembly in the sitting position, and the latch disengaging from the base for adjustment of the child support assembly between the sitting position and the recumbent position; characterized in that the actuator is pivotally connected with the backrest portion and is operatively connected with the latch via a linkage and a resilient arm, the actuator being affixed with a pin that is pivotally assembled through and is slidable along a guide slot which extends at an angle relative to a sliding axis of the linkage and is provided at an upper end of the linkage, a lower end of the linkage being connected with the resilient arm, and the resilient arm bending toward a left or a right side of the child support assembly where is disposed the latch, wherein the actuator is operable to cause upward sliding of the linkage and the resilient arm, which drives the latch to disengage from the base.