My navigation bar of my wordpress theme is set up to wp_list_pages. I'd like to display text underneath those page links.
"Home Sweet Home"
Do I need a widget to accomplish this or is it relatively simple to implement?
Yes, but you need to use a custom walker. You must modify the function that traverse the page and output the HTML. Extend the basic wordpress class and implement your function.
See this stackechange post for a code example.
Note: I suggest you to use wp_nav_menu (custom menus) instead of wp_list_page and use the item description as your sub_menu item description.