find  components\com_rsgallery2\templates\semantic\html\gallery.php


Around line 45 find this code

<div class="rsg_sub_url_single">
        <?php $this->_subGalleryList( $kid ); ?>
</div>

and either delete it or comment it out (you can paste this commented out copy below)

<!--<div class="rsg_sub_url_single"><?php $this->_subGalleryList( $kid ); ?></div>-->

If you want to use RSgallery navigation all the way, it sounds like this hack is what you need.  Otherwise, you could create a menu link to a static content item, grab the links to each of your category thumbnail pages (KIDS, CARS, AIRPLANES) and create text or image links to those pages of RSgallery2.  If you do not hide the breadcrumb feature ('pathway' in your template) your visitors will eventually be able to find the ROOT view of RSgallery2 with thumbnails and all subgalleries listed, but that is probably not bad after they have become familiar with the layout of your site.

Know what I mean?