A seat unit and child stroller assembly includes a stroller having a frame, a seat and a safety device connected to the frame for preventing a child seated on the seat from falling off; a seat unit including a seat frame, a connecting means and an operating means mounted on the seat frame, the connecting means comprising a first locking member for locking the seat frame into the safety device and a second locking member for locking the seat frame into any device except the stroller, the first locking member being shiftable between a locking status during which the seat unit and the safety device are interconnected, and an unlocking status during which the seat unit can be removed from the stroller; wherein, the operating means is set to control the first locking member only, making the first locking member shift from locking status to unlocking status.