What is the Revolution equivalent to getDocumentChildren?

<?php
$output = array();

$criteria = $modx->newQuery('modResource', array('parent' => $parent));

// You can set other criteria based on Snippet options or other data
if (empty($showUnpublished)) $criteria->where(array('published' => true));
if (empty($showDeleted)) $criteria->where(array('deleted' => false));

// you can limit the amount of memory you use by specifying the fields you need
if (!empty($fields)) $fields = explode(',', $fields);

// just getting any spaces out of comma-delimited field list
foreach ($fields as $fieldKey => $field) $fields[$fieldKey] = trim($field);

// now add the fields to the criteria
$criteria->select('id'); // id is required when retrieving objects with lazy loading
$criteria->select($fields);

$children = $modx->getCollection('modResource', $criteria);
foreach ($children as $child) {
    // here we might skip results based on permissions, for instance:
    // if the user does not have permission to "list" a Resource, skip it
    if (!$child->checkPolicy('list')) continue;

    // here you can process each child against a Chunk serving as a tpl
    // note again we are limiting the placeholders to be replaced to the specified fields
    $output[]= $modx->getChunk($tpl, $child->get($fields));
}

return implode("\n", $output);
?>

$parent = isset($doc) ? $doc : $modx->documentIdentifier;

$criteria->select($fields);

if ($fields) { $criteria->select($fields); }

$parent = $modx->getOption('doc',$scriptProperties,$modx->resource->get('id'));

<?php
if ($fields) {
    $criteria->select('id');
    $criteria->select($fields);
}
?>

<?php
$output[]= $modx->getChunk($tpl, !empty($fields) ? $child->get($fields) : $child->toArray());
?>