This seems the right time to point out that "Barbara and Bobby Black" have a certain Amanda Ros quality suggesting, to me at least, that there is more than a bit of confabulation in Weer's retelling of the events of his fifth birthday.
The painting of Uncle Joe which is somehow the inciting event of "the accident" is layered with meanings that Wolfe carefully shows Weer to have arrived at after the fact. His memory of the painting's background as reminiscent of a fairy garden seems to have come from Weer's reading The Green Fairy book at least a year later.
Just as with Weer's retelling of Smart's "Mr T" story, we're left with no certainty about which parts of the stories are "true" and which are Weer's confabulations.
This is only going to get worse as we move into the main sections of chapter four.