If I travel with children, I assume the cost of seat reservations needs to be included, if they are of an age where I need to sit with them, which is most ages up to adulthood depending on the person.

Expecting to count on the generosity of others because you didn’t pay for two seats is unacceptable behaviour.

Personally I think it should be waived if travelling with children though. In fact, seat reservations should just be part of flying but I’m showing my age.