I know this is going to sound harsh to CC, who have not created the problem, but this is my solution.
If the airline does not ensure that any under 12s are sitting with at least 1 parent then the airline should treat them as unaccompanied minors with the CC being fully responsible for their every need (safety, food, drink, toilet, nausea, etc.). If the airline is not prepared to do this then they should ensure that their IT system will reserve family seats together.
And to add another thought....
My contract is with the airlines. If they seat my child next to some strange adult and neither my wife nor I are alongside to protect my child, then the airline better do the protecting for me.
I have travelled extensively on Emirates & SAA (and other airlines within SA) and have never had a problem sitting next to my kids. SAA once upgraded my sister and her 2 under 12 kids to business class (on a flight to the US) because the computer assigned seats had been reassigned by one of the check-in staff.
That is harsh to CC!
Speaking for BA, we will always do our best to seat children under 12 next to at least one parent, providing the family turns up with sufficient time for us to be able to do something. Pitching up at check-in 46 mins before departure, with the flight about to close, doesn't exactly give us much scope.
We may not do anything at the check in stage, but if the Flight Monitor looking after the flight in the back office is alerted, he or she will usually have something sorted out by the time boarding starts. Throwing a wobbler at the check in desk or refusing to go through security will achieve nothing - except get the family taken off the flight for failing to present themselves to security in time!
While you're on the subject of "contracts", how is the airline expected to know that they're dealing with a "family" when four people turn up with four different surnames on four different bookings? It happens!
I have to say, a lot of how passengers are treated by airlines is down to attitude. If a passenger presents the "You've got to do something" attitude, it makes staff resentful. Far better to use the "please can you help us" approach!
Some of the "attitude" is a culture thing - "Freshies" from Asia very rarely use "please" or "thank you" and have a very abrupt way of asking for things - "Water! - Get Me Water!" Neither do Americans from the Northern States, whereas Texans go overboard with politeness! Most airline staff who have been around the track for a few years can recognise the difference between culture and plain rudeness - and there ain't no excuse for being rude, ever!