Nós filhos em um nó

<html>
<head>
<title>Test</title>
</head>
<body>
<ul id="ul_o">
<li>v1</li>
<li>v2</li>
<li>v3</li>
</ul>
<script type='text/javascript'>
document.onreadystatechange = function () {
  if (document.readyState === "interactive") {
    document.body.innerHTML = '<h4><code>ul</code> with <i>ul_o</i> has '+document.getElementById("ul_o").getElementsByTagName("li").length +' <code>li</code> Tags</h4>';
  }
}
</script>
</body>
</html>
bantha