Before I retired from working as a Civil Servant for the US federal government, I was active in the effort to stop international abduction and exploitation of children. My particular position and responsibilities placed me in the role of making fast phone calls on a 24 x 7 basis to a network of contacts across countries to stop flights or interdict passage at ground entry points, to prevent adults from unlawfully taking children out of or into a country, etc. I consider it one of my better assignments. I did manage to have a few wonderful moments when an attempted abduction was stopped at a land crossing or an international airport. So, I am content in that regard, even those these activities were never reported anywhere public.
We worked with representative of various country's law enforcement and intelligence services and international organizations like Interpol to share information, develop procedures and stop these practices. Along the way, we also developed new recommended, standard practices for the various countries to try to promulgate.
Included in these accomplishments was a more or less standard recommendation for minors traveling alone to have permission letters from their legal parent or guardian with contact information to permit rapid verification by officials in any foreign country. This is why I mentioned it in my post above.
We also pursued a recommended standard to require any adult accompanied by a minor to have a similar letter with permission and contact information from the other parent in the case of one parent traveling when the other parent was at home, or both parents, if the minor was without his or her parents. We extended the recommended practice to include related family members or other adult friends, in the case of a minor 'niece' or 'nephew', etc. traveling with an adult "aunt" or "uncle" or "family friend" across borders.
Adoption of these recommendations varies from country to country and within a country from one transportation carrier to another. When I last heard from former colleagues, it was making a difference in some cases. In this, I am reminded of the old saw that says: "An ounce of prevention is worth a pound of cure..."
Also, for what it is worth, I personally practice this whenever I take minor nieces or nephews on foreign travel with me, or together with my wife. I HAVE been asked for it by airline officials; not regularly, but enough to ensure that I always have the permission letter with me.
Similarly, I always carry an "ICE" document in a waterproof bag. That is a document containing important contact, consular, and personal medical information to be used "In Case of Emergency" (ICE). I use Google Translate to translate the information into the language of the countries I will be traveling in or through. As I frequently travel alone, and I do my Caminos without partners for the most part, this is essential information to carry in case you are injured or arrested for any reason.
I hope this helps the dialog.
Some of them may become your friends for a lifetime, from all corners of the world, some will make food with you in the albergues. You will make many new friends who will hug you in joined joy in front of the Cathedral, after completing a walk of life. My dream is now to take my granddaughter, 12, with me 
