A restraint harness assembly for a child safety seat includes a strap, an anchoring mechanism and a retractor mechanism. The anchoring mechanism includes a first release button operable to switch the anchoring mechanism from a locked to an unlocked state. The retractor mechanism includes a spool connected with the strap, and a second release button movable between a first and a second position for respectively unlocking and locking rotation of the spool in a direction for unwinding the strap. The first and second release buttons are engaged with each other when the anchoring mechanism is in the unlocked state and the second release button is in the first position. The first release button can disengage from the second release button when the anchoring mechanism is switched from the unlocked to the locked state, which allows the second release button to move from the first to the second position.