We booked our 10 year old son a flight from Brussels to Newark, June 24th.
We fully paid for the 'unaccompanied minor service'. Our son was staying with his grand parents in Europe.
My parents brought our son to the airport. Upon checkin the staff told them 'the unaccompanied minor fee' was not paid, although they showed a printout of the eticket clearly stating that the $150 fee + taxes +++ was fully paid.
Long story short, after debating for over an hour they finally let my son board without paying an additional 150 EUROS!
Upon arrival we found out that United had wrongly filled out the forms and as result he could not be handed over to his mom.
Since we did expect some screwed up on the airline side we had included copies of both our passports as well as a ton of additional documents such as a declaration from us who was allowed to pick him up.
On the way to Brussels he flew with a European airline .. totally no problems.
Warning to all parents .. the unaccompanied minor service from United is a joke. Beware!