I have had a few customers recently have problems accessing child tables from navigation templates. The problem is that the $sys.item in a navigation is not the same as $sys.item in a normal template. In a navigation template this is a dynamically created proxy object that handles the relationships between navons through the submenu slot. This means that the following which would work on a normal template returns no results.
$sys.item.getNodes("Child1")
On a navigation template to get the same behavior just use the following to get hold of the underlying Node object first and it should now work.
$sys.item.getProperty("nav:proxiedNode").Node.getNodes("Child1")