William Blake's preface to Milton, commonly called Jerusalem and set to a famous hymn tune by Hubert Parry, questions whether the child Jesus might have visited England.
And did those feet in ancient time
Walk upon England's mountains green:
And was the holy Lamb of God,
On England's pleasant pastures seen!
This apparently refers to an old tradition, not originated by Blake, that Joseph of Arimathea took Jesus to Glastonbury; after the crucifixion, Joseph returned, possibly carrying the Holy Grail.
Whether this actually happened is not my question.
What I would like to know is: what is the origin of the story? According to Wikipedia, Robert de Boron wrote about Joseph and the Grail, but it does not mention if he wrote about an earlier visit by Jesus himself. So how and when did the story get started?