If I was going I'd probably keep stuff in the glovebox in the car, or another less obvious place in the car (ours has secret compartments in the footwell). If you're parking next to your tent it's as good as a safe.
We used to go every year (eurocamp style) when I was young - just make sure you don't leave things out (in the tent) at night - once some people came round with knives and cut a U shape in the windows and took what they could find on the table next to the window. We didn't lose anything but people had rings, watches and passports stolen.
We put/hide stuff in the car and prefer the more remote, out of the way campsites where less chance of outsiders strolling through. I also scan our important documents and email them to myself so that if anything should happen I can easily get hold of a copy.
All campers are in the same position so as long a you're careful and don't leave valuables lying around on show, I wouldn't worry about it too much.
FRance! We camp quite a bit in the uk but usually anything valuable such as phone keys money is with us, just debating what you do with passports, also what if you all want to go swimming together as a family?? Agree campers are honest, never any probs with leaving stuff out etc but have more reservations abroad as not sure how easy it is for non campers to access sites esp those on near the beach which will attract alot of visitors. Not even sure if our glove box is lockable but will investigate as that seems a good idea for passports.
Some campsites will have safes in the office/reception area you can hire.
We leave our passports locked in the glove box of our locked car, but figure everything else is insured and replaceable. The car keys and purse/wallet are generally with us if we're not actually in the tent.
Campers are generally an honnest lot - we've never had a problem in 20+ years of camping.
This sounds so trivial but if camping abroad (tent) what do you do with your passports, money, cards keys phone etc? Do you carry them with you at all times? Do campsites have some kind of secure storage facility?
Still debating the major issues such as where to actually book so distracting myself by focusing on the minutiae!!!