Umbraco template to redirect the current page/node to its first child page/node.

RedirectToFirstChild.master

<%@ Master Language="C#" MasterPageFile="~/masterpages/BlankTemplate.master" AutoEventWireup="true" %>
<script runat="server">
	protected void Page_Load(object sender, EventArgs e)
	{
		var current = umbraco.NodeFactory.Node.GetCurrent();
		if (current != null)
		{
			var child = current.ChildrenAsList.FirstOrDefault();
			if (child != null)
			{
				var url = child.Url;
				if (!string.IsNullOrEmpty(url))
				{
					Response.Redirect(url, true);
					return;
				}
			}
		}

		Response.Redirect("/", true);
	}
</script>