No, it's not ethical at all. Family relationships should be based on love, respect, and appropriate boundaries. Such a story involves disturbing and immoral content that can be very harmful to the psychological well - being of people who come across it.
In general, it is not appropriate for mothers to directly teach their son about sex stories in a detailed way. This topic is rather sensitive and may make both parties feel uncomfortable. Usually, sex education should be carried out in a more formal and appropriate environment, such as in schools by professional educators, who can use proper teaching materials and methods.
Stories about a mother's relationship with her children can be great. Such as how a mother overcomes challenges in raising her kids, like dealing with a child's difficult phase during adolescence.
Mothers can start by using age - appropriate books on puberty and body changes. For example, they can sit down with their sons and read a book about the physical and emotional changes that happen during adolescence. This way, it's more like sharing knowledge from a neutral source rather than a personal or embarrassing conversation.
One story could be about a little kid who secretly saved up his pocket money to buy his mom a beautiful flower on Mother's Day. He walked to the flower shop all by himself and presented it to his mom with a big, shy smile. It was a simple yet very touching gesture.
There might be a story of a mother who stands up against all odds to protect her child from a dangerous situation. Maybe it's a community where there is bullying or some form of threat, and she is fearless in safeguarding her child. She becomes a symbol of strength for her child and others around. This kind of story is very inspiring as it shows a mother's unwavering love and courage.