The parents could have easily sat here for the duration of the flight if they wanted to
, Hmmm....there speaks someone who may not have sat in a cabin jump seat for 2 ++ hours.
It is not a satisfactory alternative to a proper seat. In the good 'ole days before security and fussy regulators I have hitched rides in flight deck jump seats, cabin staff seats, and on one occasion occupied the aft hold of an F27-400 (which had an unexpectedly large effect on the aircraft CoG that nearly killed us all). Flight deck jump seats are usually quite comfortable (eg VC10, L1011, B737, BAC1-11, DC3, F27, Concorde, B747 etc) but cabin jump seats are usually instruments of torture, with vertical backs and small seats. Unless things have improved enormously.