#!/usr/bin/perl -w

use strict;
use XML::Twig;

my $t = XML::Twig->new( twig_handlers => { child => \&onChild } );

$t->parse('<node id="17"><content>foo bar</content><child file="19.xml" /></node>');

sub onChild
{
   my ($t, $child) = @_;

   my $atts = $child->atts;
   $t->parsefile($atts->{file});
}