<div class="ana">
<div class="alt1">Metin-1</div>
<div class="alt2">Metin-2</div>
</div>
<script type="text/javascript">
$(function(){
$(".ana").children().css("background","red");
})
</script>
$(".ana").children(".alt2").css("background","red");
<!DOCTYPE HTML>
<html lang="en-US">
<head>
<meta charset="UTF-8">
<title>UstaDerslik</title>
<script src="http://code.jquery.com/jquery-1.9.1.js"></script>
<script type="text/javascript">
$(function(){
$(".ana").children(".alt1").css("background","red");
})
</script>
</head>
<body>
<div class="ana">
<div class="alt1">Metin-1</div>
<div class="alt2">Metin-2</div>
</div>
</body>
</html>