<li <?php if (is_page('about-us') or wp_get_post_parent_id(0) == 52) echo 'class="current-menu-item"'?>><a href="<?php echo site_url('/about-us'); ?>">About Us</a></li><li <?php if (is_page('about-us') or wp_get_post_parent_id(0) == 52) echo 'class="current-menu-item"'?>><a href="<?php echo site_url('/about-us'); ?>">About Us</a></li>