I don't believe that is true in France, or at least not back then there were laws about minimum inheritances.

Not in France. French civil law on inheritance is much more strict than common law. For example, you cannot disinherit your children.

Interesting. Can you partially disinherit them, but donating some large sum to a charity in the will, for example?

Depending on the number of children, at least half the estate will go to them, rising to up to 3/4 for more children.