Fix for Broken Submenu on Twenty Thirteen for Tablet / iPad

You’ll need to insert the following java script to functions.js at line 53 before
// Better focus for hidden submenu items for accessibility.

// Fix sub-menus for touch devices.
if ( 'ontouchstart' in window ) {
menu.find( '.menu-item-has-children > a' ).on( 'touchstart.twentythirteen', function( e ) {
var el = $( this ).parent( 'li' );

if ( ! el.hasClass( 'focus' ) ) {
e.preventDefault();
el.toggleClass( 'focus' );
el.siblings( '.focus' ).removeClass( 'focus' );
}
} );
}

Core wordpress developers coded the fix. Hopefully it will be in the next update of Twenty Thirteen.