#!/usr/bin/perl

use strict;
use warnings;
use XML::Twig;
use Data::Dumper;

my $content = do{ local $/; <DATA> };
my $twig = new XML::Twig( twig_handlers => {  'NatuerlichePerson'   => \&getPerson,} );

$twig->parse( $content );

sub getPerson{ 
  my( $twig, $pers)= @_;
  
  my $child = $pers->first_child( 'geburtsdatum' );
  #$child->cut_children;
  my $text = join '', map { $_->text if( $_->is_text || (exists $_->{'ent'})) } $child->children;
  print $text;
}

__DATA__
<NatuerlichePerson cx:dt="null" cx:ct="struct" _name="NatuerlichePerson">
                    <geburtsdatum _name="geburtsdatum">19.05.1949<cx:attrib>
                            <_index cx:dt="int">6</_index>
                        </cx:attrib>
                    </geburtsdatum>
                    </NatuerlichePerson>