**School transport vehicles** must activate the **hazard lights** when children are getting on or off. This light is used to alert other drivers that the vehicle is performing an activity that requires additional caution, such as the boarding or alighting of passengers in this case.

- The **hazard lights** are turned on in situations that require warning other drivers of a possible danger or special activity, such as when a vehicle is stopped due to a problem or when an emergency trip is being made.
- In the context of school transport, the use of hazard lights is crucial to ensure the safety of children when getting on or off the vehicle, as it alerts other drivers to take extra precautions.


Therefore, the **hazard lights** are the correct option to ensure the safety of children in these situations.