Give your children much, much more independence. Continuously berate your ridiculous daughter-in-law because she will not let the 3 yr petit-fils play out unsupervised in the village, and insists on knowing where her 8 yr old son actually is since she left him in your bloody care, and is less than content with the aforementioned Gallic shrug as a response to her heated questions.
Maybe this is just Southern France, but insist on wrapping babies in shawls and hats and lots of clothing, even though it is 25C because they will catch a cold 
As mentioned, eat and drink anything you want, but ruthlessly monitor portion control.
If you are a women (in the South of France, especially), never ever get drunk, ever. Faux pas doesn't even begin to cover it.
Believe that family is more important than anything in the world.
Cultivate grumpiness, but underneath that exterior, be quite the softy.
Shout, exclaim, wave your hands about and seem as though you are engaging in heated discourse, but actually be asking if someone could pass the salt.
I may or may not be drawing on years of dealing with DP's French family.