How does the conversation which takes place in the ballad "We Are Seven" express a kind of blurred vision or an inability to see things clearly?

Not surprisingly, this is a complex question.  It deals
with death and Romanticism, two concepts that might be interlinked to an extent, but
both of which are extremely difficult to articulate.  In reading any poetry, I think
that it's important to try to find what you see in the poem and base your answer off of
this.  With this in mind, I hope you can take what is here as a guide or a springboard
for further thought.

Fundamentally, I think that Wordsworth
wants a "blurred vision" to result from the conversation about death. The speaker
believes that life ends when one is buried.  The child does not.  This is where the
"blurred vision" comes from:  The discussion of death is a blurred one.  Being a
Romantic thinker, Wordsworth likes the idea of children expressing universal truths that
"see into the life of things."  Wordsworth is the thinker who coined the phrase, "The
child is the father of the man."  In this light, one sees a collision between
Enlightenment values and Romantic ideals regarding the issue of
death.

For the literary and intellectual generation that
preceded Wordsworth, when life ended, it ceased to exist.  When someone physically dies,
their lives are over.  They are buried, and the matter is closed.  This would be the
thoughts of the speaker who says that there are only five children in the family with
the two that are dead.

For the Romantics, though, the issue
of death is a beautiful one because it opens up the unknown, the uncertain, and allows
ambiguity and doubt to create thought and passion.  It is here where Wordsworth feels
the child challenges the conventional wisdom with her belief that the two siblings are
in fact in existance.  The girl is articulating the idea of a soul or some type of life
force that goes beyond what is quantifiable, physical or real.  It is here where the
Romantics would embrace what the child is saying and try to use it to go against the
materialist and empiricist view of reality.

Within this
dialogue is where the "blurred vision" takes place.  One can either dismiss the child as
slightly off her rocker or the speaker for being too cold, but in either case the
speaker is left wondering and is challenged by the "blurred vision" that is present. 
Yet, it is precisely in this lack of definitive answers or clarity where Wordsworth
would feel that any search for understanding must lie.  Out of this "blurred vision,"
Wordsworth would argue, a stronger and more coherent understanding
emerges.