WordPress: Add New Menu Navigation with dynamic child category walker class

functions.php

//* Add New Menu Navigation  with dynamic child category walker class
add_action( 'genesis_after_header', 'webendev_subcat_navigation', 15 );
function webendev_subcat_navigation() {
	echo '<nav class="nav-primary">';
		wp_nav_menu(
			array(
				'container_class'	=> 'wrap',
				'theme_location' 	=> 'primary',
				'menu_class'      	=> 'menu genesis-nav-menu menu-secondary',
				'walker' 			=> new Submenu_Walker_Nav_Menu()
			)
		);
	echo '</nav>';

}