customizing html in PHP menu constructor

I am creating a custom theme for a client and am having trouble figuring out how to wrap a <div> around the top level link, and wrap the linked text in a span, but only for the parent pages in my navigation menu, like this

<li id=&quot;community&quot;>
	<div class=&quot;parent&quot;>
		<a href=&quot;#&quot;><span>Top Level Page 1</span></a>
	</div>

	<ul>
		<li><a href=&quot;#&quot;&quot;>Sub Page 1</a></li>
	</ul>
</li>

I’m a designer, and know very little about PHP constuctors.

I am working in the classes.php, but can’t figure out how to get it to treat the parents differently from the children. Can anyone offer me some guidance.
Thank you,