How to find a child div which isn't hidden
===

I have the code:

<div id="parent">
   <div id="firstchild" style="display:none">
   <div id="secondchild">
   <div id="thirdchild" style="display:none">
</div>

So what I want to do is find the element in jquery that isn't hidden ie. secondchild.

I'm guess I sould use something along the lines of :hidden but I'm actually wanting to do the opposite and find the non hidden one.

Would anyone know how to do this? To find the visible div that is a child of parent and make it hidden?