Final answer:
The specific annual number of parents murdered by their children in the U.S. is not provided, but discussions around family structures and issues such as firearm accessibility relate to the underlying factors of domestic violence.
Step-by-step explanation:
The number of parents murdered by their own children annually in the U.S. is not a widely reported or specific statistic available for reference in the general literature, including the details provided. However, discussing family dynamics and societal issues such as family structure and child abuse may relate indirectly to the factors contributing to such grave outcomes. For instance, according to census data, the nuclear family structure has seen a decrease, with only 66 percent of children living with two married parents, which could be a stressor in the family dynamic. Moreover, the ease of accessibility to firearms also plays a role in the incidence of violence, as seen in school shootings.