Student Exchange Programs

I am going to be a foreign exchange student in France for a very short amount of time (a little more than two weeks). I will be staying with a family consisting of two grandparents and a 16 year old granddaughter. What should I get the family as a gift? And what should I get for the girl?

And do you have any other suggestions or comments about things such as cultural differences? (i.e. do’s and do not’s)

Thanks!