Thanks Matt Varone on this function to check if the current page is a subpage. WP should have made this a core function
http://www.mattvarone.com/wordpress/is_subpage-function/
A useful companion item is to create a template for a parent page where you only want to redirect it to the first subpage. Sometimes you don’t want a page for the parent at all, just the children.
From WPRecipes:
http://www.wprecipes.com/wordpress-page-template-to-redirect-to-first-child-page