Managed to find the right approach just now using Google which came up with this page
which led me to alter the above attempt to...
<% if ChildrenOf(about-us) %>
<% control ChildrenOf(about-us) %>
<li class="$LinkingMode"><a href="$Link" title="Go to the $Title page">$MenuTitle</a></li>
<% end_control %>
<% end_if %>
which appears to work, just in case anyone else is stuck for this kind of control. Kinda odd none of the SS team could help on this one?
Obviously with a free open source CMS I don't expect to be spoon fed, people are busy - we all are - but a bit of a guiding hand in the shape of better documentation/tutorials that cover a bit more than the five that come with the set up would really help this project as it's a lovely CMS from a end user POV and I think very flexible given the experience and more verbose easy on the brain step through docs being made available.
Feel that I am on a very steep learning curve at the moment and not much in the way of a safety net.