Truthfully, though, I think that there is a difference between two "not street smart" people when one of them has food allergies.
DD has an awareness of her surroundings that is really unsurpassed even by my DH, who grew up in a city environment and is by every indication "street smart."
I think most kids who grow up with food allergies do have that awareness of other people around them, if that makes sense. They are really in tune with human behavior and body language/nonverbal cues.
I noticed this with my DD (13yo) and one of the 18yo students on this trip-- had a chance to observe them both together in Paris, and while there was superficially almost nothing that separated them-- same type of day bags, same basic body postures, roughly the same size... and roughly similar interests and maturity levels, my DD had this, I don't know... casual, relaxed sort of ALERTNESS about her that the other girl seemed to lack. There just wasn't any indication that my DD was consciously doing it, but she seemed far more aware of it all-- she was able to walk WITH the pedestrian flow seamlessly while sightseeing, able to match the pace and know how to be out of the way or dart quickly through a crowd to catch a train, that kind of thing.
I don't know if I can explain it better than that. She was clearly aware of what others were doing around her without gawking or looking nervous (which marked many of our tour group as inexperienced). I attribute that wariness to YEARS of paying attention to what others are eating, where they are putting their hands, etc, without being rude about it.
It was quite an interesting thing to watch. Some kids had it naturally, and some didn't.
That seemed (from our observations) to be what separated those that got targeted by pickpockets and those that did not-- we did see groups of them working in Paris, and who they were watching most closely. It certainly wasn't experience alone, because my DD has not spent much time in urban settings, and nearly NEVER on public transportation or in that kind of crowding.
I don't know that all FA teens could translate that life experience from the one domain to a more general one, but it might help to consider it. I suspect that it is a skill that many of them have.
Or just do what Rick Steves advises-- carry nothing much of value in your day bag-- bottled water, snacks, a guidebook, that kind of thing. Nothing irreplaceable.