In the movie "The American President" Sydney Ellen Wade (Annette Benning) hurls abuse at President Andy (Micahel Douglas) for legislation to "keep Uzis out of the hands of 8 year olds".
In Real Life such legislation - if it exists - didn't work. But somehow if a "responsible adult" allowed an 8 year old to have a loaded machine pistol that's alright.
The US constitution does allow the "right to bear arms" but only to provide for a citizen militia. In any event the Bill of Rights is a series of Amendments - in other words the founding fathers recognised that the constitution being a human creation is imperfect. And thus mutable. It may not be always right and can and should be changed.
How many more innocents have to die before the NRA wakes up?