If you pass ForceArray to XMLin() you should get equivalent XML for both $xml_src and $xml_out e.g

my $xml_src  =
'<foo>
  <bar><number>1</number><foobar>Hello world</foobar><barfoo>Goodbye w
+orld</barfoo></bar>
  <bar><number>2</number><foobar>abc</foobar><barfoo>def</barfoo></bar
+>
</foo>'
;

my $xml_in = XMLin($xml_src, ForceArray => 1);
my $xml_out = XMLout(Test(), rootname=>'foo');

print "Source:\n" . $xml_src . "\n\n";
print "Output:\n" . $xml_out . "\n";

sub Test{
  my $entry;
  my $out;
  foreach $entry(@{${$xml_in}{'bar'}}){
    push @{${$out}{'bar'}}, {%$entry}
  }
  return $out;
}

__output__

Source:
<foo>
  <bar><number>1</number><foobar>Hello world</foobar><barfoo>Goodbye w
+orld</barfoo></bar>
  <bar><number>2</number><foobar>abc</foobar><barfoo>def</barfoo></bar
+>
</foo>

Output:
<foo>
  <bar>
    <number>1</number>
    <barfoo>Goodbye world</barfoo>
    <foobar>Hello world</foobar>
  </bar>
  <bar>
    <number>2</number>
    <barfoo>def</barfoo>
    <foobar>abc</foobar>
  </bar>
</foo>
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