The United States, which has an English common law tradition, the concept of a right to keep and bear arms was recognised prior to the creation of a written national constitution.It's scary that people feel they need to arm themselves to protect their families, the more people are armed the worse the situation becomes. It's supposed to be a civilised country yet it could turn into the wild west.
I hope your son and his family stay safe as well as everyone else who just wants a normal life without the threat from armed idiots, many of which are organised.
When colonists in the Thirteen Colonies rebelled against British control during the American Revolution they cited the 1689 English Bill of Rights as an example.
It was those colonies that came together to form the United States. The original 13 colonies of North America in 1776, at the United States Declaration of Independence.