Pressing the button of the front outside door handles with all doors (and tailgate) closed and any door unlocked, locks all the doors (and tailgate). The hazard warning lights will blink once to indicate that all doors (and tailgate) are locked. The button will only operate when the smart key is within 0.7 ~ 1m (28 ~ 39.3 in) from the outside door handle. If you want to make sure that a door has locked or not, you should check the door lock button inside the vehicle or pull the outside door handle.
Even though you press the button, the doors will not lock and the chime sounds if any of the following occurs:
Kia Niro 2017 (DE HEV) Service Manual: Engine Coolant Temperature Sensor (ECTS) Schematic diagrams
Circuit Diagram
ECTS [Water Temperature Control Assembly]
Harness Connector
ECTS [EGR Cooler Tube]
Harness Connector
...
Kia Niro (DE HEV) Owners Manual: Our recommendation: Children always in the rear
WARNING
Always properly restrain children in the vehicle. Children of all ages are
safer when riding in the rear seats. Never place a rearward-facing Child Restraint
System on the front passenger seat, unless the air bag is deactivated.
Children under age 13 should always ride in the rear seat ...