At what point in the novel, The Boy in the Striped Pajamas, does Bruno lose his innocence?What happens, that ends his innocent perspectives? Does...

In my mind, the moment that Bruno changes his clothes and
hops the fence is when a point of innocence is lost.  I say this because it is at this
point that Bruno has done a couple of things that represent a narrative of experience as
opposed to innocence.  The first would be the disobedience of his father's instructions
to not go to certain parts of the camp.  The edict of "Out Of Bounds At All Times And No
Exceptions" is completely discarded when Bruno crosses the fence.  While it is valid
that he had already tested out this maxim by actually approaching the fence, the notion
of crossing it, of violating the demarcation of what is accepted and forbidden,
represents a moment of experience supplanting innocence.  Along these lines, the
changing of clothes might be a symbolic moment where innocence becomes replaced with
experience.  Bruno empathizes with Shmuel enough to be able to move his frame of
reference into his.  In its purest of terms, this is no longer innocent, complete in
one's own self- absorption.  Rather, it is an act of maturation and insight for Bruno to
not only walk in another's shoes, but wear their clothes and absorb their experience.
 There is probably a loss of innocence at the moment that Bruno recognizes something
being wrong as he and Shmuel are herded into the gas chambers.  To probe into Bruno's
mind at that moment would be a loss of innocence as he either realizes the dire
consequences of what is to be or fully grasps the faith in his friendship as a way to
ward off the horror of what is to be.