Originally Posted by
carrotjuice
Emergencies can happen anytime, not only during take-off and landing - hence if I was a passenger witnessing children fussing about the emergency exit, I would highlight to the purser. Crew that allow this are simply irresponsible.
Emergency exits can only be used on take-off and landing. They are of not much use (and indeed are physically impossible to open) at other times of the flight. Therefore some airlines do allow kids to sit there during cruise only, though I agree the reasoning may not be obvious to most passengers.