When having a parent and a child page in a navigation and the parent has a url, there is no way to expand the parent to show the children on a mobile device. Each time the parent is clicked, it will redirect to another page.
How to make the children menu expand when clicking on the expand arrow and preserve the redirecting to another page when clicking on the title.

The following code will make the menu expand when hovering over the parent. This case is not applicable for mobile devices.

<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="ResponsiveNavigation.ascx.cs" Inherits="SitefinityWebApp.Custom.Widgets.Navigation.ResponsiveNavigation" %>
<%@ Register Assembly="Telerik.Sitefinity" Namespace="Telerik.Sitefinity.Web.UI.NavigationControls" TagPrefix="sfMap" %>
<sfMap:SitefinitySiteMapDataSource runat="server" ID="SitefinitySiteMapDS"  ShowStartingNode="false" StartFromCurrentNode="false"/>
<div class="simpleMenu">
         <telerik:RadNavigation runat="server" ID="SimpleMenu" DataTextField="Title" DataValueField="ID" DataSourceID="SitefinitySiteMapDS" OnClientNodeMouseEnter="OnClientNodeMouseEnter"
                OnClientNodeMouseLeave="OnClientNodeMouseLeave"/>
</div>

<script>
    (function () {
        var timeOut;
        var isMouseOverNode = false;

        window.OnClientNodeMouseEnter = function (sender, args) {
            var node = args.get_node(),
            expandedSubling = node.get_parent().get_expandedNode();

            if (node.get_hidden()) {
                return;
            }

            clearTimeout(timeOut);

            if (node.get_expandedNode()) {
                node.get_expandedNode().collapse();
                return;
            }

            if (expandedSubling && expandedSubling !== node) {
                expandedSubling.collapse(true);
            }

            if (!node.get_expanded()) {

                node.expand();
            }
            isMouseOverNode = true;
        };

        window.OnClientNodeMouseLeave = function (sender, args) {
            var $ = $telerik.$,
            node = args.get_node(),
            event = args.get_domEvent();

            if (node.get_hidden()) {
                return;
            }

            isMouseOverNode = false;

            if ($(event.relatedTarget).closest(node.get_animationContainer()).length > 0) {
                return;
            }

            timeOut = setTimeout(function () {
                if (!isMouseOverNode) {
                    if (sender.get_expandedNode()) {
                        sender.get_expandedNode().collapse();
                    }
                }
            }, 300);
        };
    })();
</script>

The following script should be added in order to expand the menu when clicking the expand arrow.

$('.radIcon').click(function (event) {
    event.preventDefault();
});