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You could use conditional statements to show the children. Depending on what your using to categorize the pages…

If you were using parent / children categories it would work something like this:

<?php 
     if ( in_category( 'New Watches' )) {
          // show new watches menu
     } elseif ( in_category( array( 'Classic Watches' ) )) {
         // show classic watches menu
     } 
?>