source & explanations: http://modxcms.com/forums/index.php/topic,61271.0.html

snippet.getChildren.php

<?php
// First fetch all the children of the current resource
  $children = $modx->resource->getMany('Children');
  // Check if there are any. If not, return false
  if (!$children) { return false; }
  // Check if there is a tpl set, if not return an error
  $tpl = $modx->getOption('tpl',$scriptProperties,'');
  if (!$tpl) { return 'No template given.'; }
  
  // Start the output
  $o = '<h2>[[*pagetitle]]</h2><ul>'; 
  // Look through the results...
  foreach ($children as $child) {
    // ... fetching the needed info...
    $out = array(
      'id' => $child->get('id'),
      'pagetitle' => $child->get('pagetitle'),
      'menutitle' => $child->get('menutitle'),
      'longtitle' => $child->get('longtitle'));
    // ... and adding it to the output as placeholders in the chunk
    $o .= $modx->getChunk($tpl,$out);
  }
  // Don't forget to close the list
  $o .= '</ul>';

  // Return the output
  return $o;