Q:

How to target second child element of a div using JAVASCRIPT

I'm not sure if this is possible, I rarely do when I ask questions on this site, but everyone keeps telling me to use jQuery to do so. I make websites, but I am VERY novice at all of this and would prefer to get solid grip on Javascript before moving forward.
Anyways, my question is "Is it possible to target a second child (i.e. 
<div>
   <div></div>
   <div></div> <!--This one-->
</div>

using JAVASCRIPT in order to manipulate it? If so, how?" 
My previous attempt didn't work, I had a strong feeling it wouldn't but, all the same. 
function activateEvent(obj) {
    obj.secondChild.style.display="block";};

A:

obj.firstElementChild.nextElementSibling

(doesn't work in IE8)
Or
obj.children[1]

