sub get_children {
  my $parent_id = shift;

  $executed_handle = $prepared_handle->execute($parent_id);

  # first retrieve all the results
  my @results;
  while (my $pointer = $executed_handle->fetchrow_hashref) {
    push @results, $pointer->{parent_id};
  }

  # now deal with the results
  foreach (@results) {
    $results .= $_."\n";
    get_children($_);
  }
}