What requirement must be met for two children to share a single seat?

The requirement that must be met for two children to share a single seat is that the combined weight must not exceed 77kg. This standard is in place to ensure the safety and comfort of all passengers during a flight. When children share a seat, it is important to consider both their physical size and weight to ensure that they can sit safely in that space without compromising seating regulations or safety protocols set by the aviation authority.

Selecting this criterion allows airlines to maintain safety measures and to ensure that the load and balance of the aircraft are properly managed. It's important for airlines to have guidelines that prevent larger children from sharing seats with smaller children, as this could lead to issues during turbulence or in the event of an emergency.

In situations where sharing a seat is permitted, the weight limit is a crucial factor as it directly impacts the safety and operational considerations of the flight.