In the good old days when schools were not available in various outposts on BOAC/BA routes, the start and end of UK boarding school holidays were marked by the UM specials, dreaded and avoided by staff and adult passengers alike. IIRC they carried extra female warders for disciplinary purposes; they dressed as additional cabin staff, but that fooled no-one. (Then as now, it was sometimes hard to spot the difference between HMP and BA staff in any case.)
Extra handling staff were needed to herd them off and on the aircraft and through the airport, corralling them when a wait was needed. God, that was terrifying enough, but the 6-hour flight that followed must have been a real challenge for the crew.
PS Why is the thread title "Accompanied Children"?