no, I would not give teenagers their passports to carry, I just think there's too much risk of losing them. I can't think of any reason why they would have to have a passport with them. If they get into trouble somehow with the law or something (which I'd worry more about how that would happen), they can call you to bring them.

YOu might want them to carry around the phone numbers for local police or medical help, and a taxi, here they are:

Police 17
Pompiers 18 (fire/accident)
SAMU 15 (for medical emergencies)

Eng-speaking taxis:
G7 taxis 01-47-39-47-39
Taxis bleu 01-49-36-10-10

The gen. European emergency no. is 112 now (like US 911), but I'd probably use the Paris 15 or 17 -- don't know which would be better.

For your own use, the SOS Medecins (24 hr emergency doctors who will do house calls) phone no. is 01-47-07-77-77. For a real medical emergency, use the SAMU phone no. 15.

oh, I forgot one, the English-speaking help/crisis line is 01-47-23-80-80

I think it's a good idea for everyone to carry around a few of these numbers in Paris, I always have police, SAMU, and taxi numbers.

Everyone should carry a COPY of their passport with them at all times. French law requires that you have identification if requested.