What does the last quote "Nothing like that could happen again. Not in this day and age" represent?

I think that the last quote is where Boyne's voice emerges
throughout a narrative where Bruno's voice was heard.  At the end, when Bruno dies, the
eyes and perception that led us throughout the narrative is also gone.  It is up to
Boyne to be able to provide some level of both closure and testament to Bruno in the
process.  The last quote is able to do this and also strike the reader on two levels. 
The first is that there has to be some reckoning between Boyne's statement, which
presents consciousness as it should be, and our own reality, which sadly does fall short
of this standard.  The conditions in which we live are ones where there are still
examples of genocide happening.  There are situations where children are being murdered,
no different than Bruno and Shmuel, and we, as the reader, must account for it in
reflecting on the last quote.  The second level in which the quote impacts the reader is
that while it is Boyne's voice speaking, he has managed to continue the child's faith in
the world and the child's viewpoint that has constructed the novel. For Bruno, his
transcendent views of the world are able to rise above the horrible contingency of
Nazism in the closing words of the novel.  In suggesting that something like the
Holocaust or what happened to Bruno and Shmuel should never happen again, we, as the
reader, are left to see the world, our world, as Bruno would.  While we have to reckon
with the differences between Bruno's vision and how our world is, Bruno gives us a
standard to which we are compelled to aspire.