Пример:
Найти все элементы, являющиеся «детьми» элементов с id "main".
"HTML"
<span id="main">
<div></div>
<button>Child</button>
<div class="mini"></div>
<div>
<div class="mini"></div>
<div class="mini"></div>
</div>
<div><button>Grand</button></div>
<div><span>A Span <em>in</em> child</span></div>
<span>A Span in main</span>
</span>
"CSS"
body { font-size:14px; }
span#main { display:block; background:yellow; height:110px; }
button { display:block; float:left; margin:2px;
font-size:14px; }
div { width:90px; height:90px; margin:5px; float:left;
background:#bbf; font-weight:bold; }
div.mini { width:30px; height:30px; background:green; }
"Живой пример jQuery"
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<link href="http://slyweb.ru/css/jqueryiframe.css"
rel="stylesheet" type="text/css"/>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.5.0/jquery.min.js"></script>
<script>
$(document).ready(function(){
$("#main > *").css("border", "3px double red");
});
</script>
</head>
<body class="iframe">
<span id="main">
<div></div>
<button>Child</button>
<div class="mini"></div>
<div>
<div class="mini"></div>
<div class="mini"></div>
</div>
<div><button>Grand</button></div>
<div><span>A Span <em>in</em> child</span></div>
<span>A Span in main</span>
</span>
</body>
</html>
<style>
body { font-size:14px; }
span#main { display:block; background:yellow; height:110px; }
button { display:block; float:left; margin:2px;
font-size:14px; }
div { width:90px; height:90px; margin:5px; float:left;
background:#bbf; font-weight:bold; }
div.mini { width:30px; height:30px; background:green; }
</style>