I believe I once read (a long time ago)
that I read a short story about a young native american, with his father (or grandfather) witnessing the first spanish
explorers coming ashore in N. America. I haven't been able to find it since, though
my memory (faulty at this age) was that it
was in an Bradbury anthology of short stories
Can anybody help me?

The story is "Perhaps We Are Going Away."

The story is in "The Machineries of Joy"