I bet there are some grieving parents of kids kidnapped by estranged parents who fervently wish that this was a cast-in-stone requirement for all air travel and ground border crossings. Interesting to read this and think back. Eighteen years ago, I travelled alone from Canada to the Southern US with my 2 and 4 year old children to visit relatives. Not a seasoned traveller back then. Didn't think of taking a letter. My toddler/preschooler were quizzed at length by border control about where we were going (to visit Auntie and cousins), where was Daddy (working), etc. etc. They finally let us travel. Phew! After that, always made sure every under-19 coming across any border with me had an appropriate letter. And was never asked again to produce it.