I was 5 and I have only a vague jumble of memories regarding this event. I do remember being of an age where it was seriously shocking to me, the idea that a president wasn’t invulnerable. I was a bit disturbed by seeing the chaos and the emotional upset of the adults of the world (which is never a good thing to a kid.. if the adults are freaking out, you know it’s bad news).
I was aware of the concept of assassination at that age, but up until Reagan, it was a thing of historical lore (i.e. Lincoln). That was kind of shocking, too. I had no concept of politics or party lines; to me, as a kid, our president was simply our president and, as such, was to be listened to and respected. I remember being in disbelief, like, WHY would anyone do that?