A child safety seat assembly includes a support base, and a child carrier operable to detachably assemble with the support base. The support base has a shell body that defines a receiving area and includes an upright surface raising upward from a bottom surface, the shell body being assembled with a latch located adjacent to the upright surface. The child carrier includes a seat shell having a foot portion protruding downward, the foot portion having an interior in which are assembled a release arm and a fixed rod. The foot portion is placed on the bottom surface in the receiving area and the latch engages with the rod when the child carrier is locked with the support base, and the release arm is operable to push the latch to disengage from the rod for removal of the child carrier from the support base.