show first ul that have li

show first ul that have li

Simple question I have a list like this
<div class="ullist">
<ul></ul>
<ul></ul>
<ul></ul>
<ul>
<li>child1-1</li>
</ul>
<ul>
<li>child2-1</li>
<li>child2-2</li>
</ul>
<ul></ul>
</div>
And it is set with css to hide all uls within div. I want to unhide the
first ul that has children li's.
How to do this with jquery correctly?