Show child div on mouse hover of parent - needs javascript?

@jdln; yes

css:

.outer {
    background:red;
    height:100px;
}
.box1 {
    background:blue;
    height:100px;
    width:80px;
    display:none;
}
.outer:hover .box1{
    display:block;
    cursor:pointer;
}

check the fiddle: http://jsfiddle.net/sandeep/XLTV3/1/

No JS required.

.hidden {
  display: none;
}

.parent:hover .hidden {
  display: block;
}

<div class="parent">
  <p>Hello, I'm a child...</p>
  <p class="hidden">..and so am I but I'm hidden.</p>
</div>