[jQuery] Find a specific children in a jquery object

[Giovanni Battista Lenoci]

Hi, if I want to get the ul childrens of a li element I do something
like this:

$('#li_id ul')

But If I have already the jquery li object how can I do this without
getting the id of the element?

More in specific, I click on a checkbox, then I get the container
(which doesn't have an id) with parent() method, then I want to know
if in the parent exist an ul element.

<ul>
<li>
  <input type="checkbox" id="check1" value="1" name="test"
class="checkall" />
</li>
<li>
  <input type="checkbox" id="check2" value="1" name="test"
class="checkall" />
  <ul>
     <li><input type="checkbox" id="check3" value="1" name="test"
class="sub_check" /></li>
     <li><input type="checkbox" id="check4" value="1" name="test"
class="sub_check" /></li>
  <ul>
</li>
</ul>

then in jquery I do:

$('.checkall').bind('click', function () {
  parent_li = $(this).parent()[0];
  // now I want to know if parent li has ul inside.
});

Thank you