According to my French
teacher, who grew up in Normandy
sometime between 1950 and 1970 (I assume...), you're always supposed to call people in your family tu
. This, besides including your parents, aunts, uncles, and grandparents, would even apply to people you've never met before but who are understood to be related
to you. There is also a trend in Quebec
to for students to call their teachers tu
as a token of the more human relationship that students have with their teachers.
It should also be noted that in children's TV shows and movies (such as dubbed versions of Disney animations), vous is simply not used. It's always tu.
: Heh, actually, this teacher did mention that as well. In "les familles très aristocratiques", she said, they still call everyone vous