compare that with the black candy theme for layout/Page.ss.
There should be something like...
<% include SideBar %>
this says "include side bar" (err, yeah), then in includes/SidBar.ss there should be something like...
<ul id="Menu2">
<% control Menu(2) %>
<% if Children %>
<li class="$LinkingMode"><a href="$Link" title="Go to the $Title.XML page" class="$LinkingMode levela"><span><em>$MenuTitle.XML</em></span></a>
<% else %>
<li><a href="$Link" title="Go to the $Title.XML page" class="$LinkingMode levela"><span><em>$MenuTitle.XML</em></span></a>
<% end_if %>
<% if LinkOrSection = section %>
<% if Children %>
<ul class="sub">
<li>
<ul class="roundWhite">
<% control Children %>
<li><a href="$Link" title="Go to the $Title.XML page" class="$LinkingMode levelb"><span><em>$MenuTitle.XML</em></span></a></li>
<% end_control %>
</ul>
</li>
</ul>
<% end_if %>
<% end_if %>
</li>
<% end_control %>
</ul>
<div class="clear"></div>
and this code says, for each child page show a link (and if current page is one of these children, then show it's children too).
My guess is that higher ground doesn't implement this...