My daughter flew to canada aged 12 not as a UM and the check in staff were not sure that she was allowed to be and had to check with the supervisor.
Kindly they asked the cabin staff just to keep a eye on her!
She was not being met by a parent so she had a letter signed by both parents not notarized and she had details of her medical insurance.
Then on return at immigration at T5 an immigration officer did telephone me in the arrivals hall to check that I was there and to confirm who I was and they asked her where she had been - they explained to me it was about trafficing and I am happy that they look out for children. The photographs in childrens passports are often so generic it would be very easy to use a passport to bring in a different child.