When widowed Mom discovers her young son is exceptionally well hung, she fears that he could permanently injure young girls and also be called a freak by those who avoided penetration. She calls her family Dr. to have her son examined and gets the best advice she's heard since her husband died.
After Dad is killed, son takes charge as timid mom surrenders control. He eventually coats her vaginal walls with incestuous sperm and makes her his woman.
Time and circumstances set the stage for a dependent widowed mother to finally have her mature for his age son's root buried in her bush. She says, "We can't." He says, "Who's going to know?" "Nobody, I guess but don't ever tell anyone I let you."