How to vertically align two or more (side by side) elements in a div?

I am trying to vertically align two elements with different heights in a div:

<div class="footer-icons">
    <div id="footer-twitter">
         <img src="images/twitter.png" width="40" alt="">    
    </div>
    <div id="footer-fb">
         <div class="fb-like" data-href="http://facebook.com/user" data-send="false" data-layout="button_count" data-width="160" data-show-faces="false" data-font="arial"></div>
    </div>
</div>

The twitter div has a height of 40px, and the fb div has a height of 20px. What is currently happening is the fb div is vertically centered with the bottom edge of the twitter image. Here's the CSS:

.footer-icons {
    padding-top:40px;
    width:300px;
    margin:auto;
    text-align:center;
    vertical-align:middle;
}

#footer-twitter {
    display:inline-block;
}

#footer-fb {
    display:inline-block;
}

What am I doing wrong?

Solution

Put the vertical align on the inner divs

#footer-twitter{
  display:inline-block;
  vertical-align:middle;
}

#footer-fb{
  display:inline-block;
  vertical-align:middle;
}