The online check-in can be fixed by ensuring that, when the u/c (unaccompanied child) reservation is made, the adjacents seats are blocked out. Any computer can do that - if the company thinks about it.
As to sitting alongside - I have had some right boring people. Last year I spent 12 hours next to a man who did not understand that if a person is using his iPod (prominently displayed for his education) AND is reading a book AND deliberately waits until he is tapped on the arm for the second time
before looking up - then he doesn't want to be disturbed!! Besides he was obese and overflowed the seat - and a PE seat at that!!
As
LondonPax suggests, the u/c will probably get on with the games and video. And if CC cannot spot someone manoeuvring, or following, or 'casually' hanging around a child - then they are not the observant people they should be. There is no problem here and I think the article states it very well, hence listing it here.