Dropdown menu with and without spans

Hey!
I am trying to create a drop down navigation generated from the WordPress ‘wp_list_pages’ tag. Does anyone know if its possible/how to add spans to the parent links and no spans to the children links.

I need it to look like this:

• <span>Parent Link1</span>
• <span>Parent Link2</span>
• <span>Parent Link3</span>

• Child link1
• Child link2

I am currently using

<?php wp_list_pages(‘title_li=&sort_column=menu_order&link_before=<span>&link_after=</span>&depth=2&title_li=&exclude=91,39’); ?>

I really appreciate any help!

Thanks
Hanna