div#test p:first-child {text-decoration: underline;}
div#test p:last-child {color: red;}

http://www.quirksmode.org/css/firstchild.html

The :first-child pseudo class means "if this element is the first child of its parent". :last-child means "if this element is the last child of its parent". Note that only element nodes (HTML tags) count, these pseudo-classes ignore text nodes.

CSS Pseudo Classes

CSS