If I may pick up the baton for tightslot ? There is no suggestion that the rules are not the rules, however I completely agree that there are circumstances when a significant degree of both common sense and compromise should prevail, and some of those have been highlighted here.
A child over two tears of age ( at the time of travel ) should occupy a seat and it is incumbent upon those responsible for check in and boarding to ensure that is complied with. Accepting that mistakes happen it falls upon the crew to ensure compliance. That compliance however becomes difficult if the suspicion is not aroused prior to departure and is practically redundant once airborne.
In flight if a young child over 2 will not occupy a seat and the parents cannot or will not enforce compliance then clearly there has to be a sensible compromise, unless you want to fly around in circles arguing the point, which obviously is an option. Neither tightslot nor I are in any way advocating a violation of the statute on this matter, however there are certain circumstances where common sense must prevail and as a captain I would in those circumstances both condone and if required support tightslots response or any member of the crew that had to make a mature considered decision in such difficult circumstances.
Obviously I appreciate others might disagree and they would certainly have the relevant sections of the act to support their case, but I can find other sections to argue my own if need be.