simplexml-addchild.php

<?php

class MySimpleXMLElement extends SimpleXMLElement {

  public function addChild($name, $value = null, $namespace = null) {
    $result = parent::addChild($name, null, $namespace);
    if (isset($value)) {
      $node = dom_import_simplexml($result);
      $node->appendChild($node->ownerDocument->createTextNode($value));
    } 
    return $result;
  }
}

$element = new MySimpleXMLElement('<foo/>');
$element->addChild('bar', 'A & B');
$element->addChild('bar', 'C & D');


echo $element->asXml();