Understand you are unfamiliar with the rules but you need the travel documents at the start because if you have issues UA is responsible to return you to your point of origin at their cost.

There is no grounds for compensation because you were not aware of these rules.

Important issue --- make sure your son's ticket to UK is still active.

Also see http://www.flyertalk.com/forum/unite...ec-2013-a.html -- the non-stop limitation is common among the majors.