SHOULD I TELL MY DAUGHTER IN LAW?

Recently my elder son got married. My daughter in law is well mannered and well cultured. But the thing is that she wear saree below navel it is too below. Our relatives come, what I am observing that the male members including my brother in laws all are 60+ they stare at my daughter-in-law's navel. She has a deep and round navel.When ever i try to explain her she said that she is not bothering of all this thing. The problem is that even my younger son also look her navel and the most disgusting thing is that my husband is also not exception. I also wear saree but my husband did not care. How should I handle this situation?