Hello, please follow this sample:
Parent page:
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<script type="text/javascript">
function alert_me() {
alert('hello this is parent');
}
</script>
</head>
<body>
<iframe src="iframePage.aspx" width="800px" height="600px">
</iframe>
</body>
</html>
Iframe Page( Child Page):
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<script type="text/javascript">
function ClickMe() {
parent.alert_me('hello there!');
}
</script>
</head>
<body>
<br/>
<br/>
<input type="button" value="Click me" id="button_click" onclick="ClickMe()"/>
</body>
</html>