Click on the sites link in the SharePoint portal Server top nav and you
will see all the top level sites added via that portal (or manually
added to the Sites list) categorized on the Sites Directory Area.
Once on a child Site, you can click on site Settings in the top nav (or
in the smart menu on Meeting Workspaces - Multi-
Page Sites) and then click on Manage Sites and Workspaces to see all the
immediate child sites. You can also see the entire site collection by
clicking View site hierarchy near the bottom of the Site Administration
page. There are other ways to view child sites but these are the two
most common.