The classes changed from Bootstrap 2 to Bootstrap 3
The date range markup in the docs is out of date for bootstrap 2:
<div class="input-daterange">
<input type="text" class="input-small" />
<span class="add-on">to</span>
<input type="text" class="input-small" />
</div>
But if you go to the online demo with input ranges, you can see the correct markup:
<div class="input-daterange input-group">
<input type="text" class="input-sm form-control" />
<span class="input-group-addon">to</span>
<input type="text" class="input-sm form-control" />
</div>
Demo in Stack Snippets
<!-- begin snippet: js hide: false -->
<!-- language: lang-html -->
<link href="//cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.2/css/bootstrap.css" rel="stylesheet"/>
<link href="//cdnjs.cloudflare.com/ajax/libs/bootstrap-datepicker/1.3.1/css/datepicker.css" rel="stylesheet"/>
<script src="//cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.2/js/bootstrap.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/bootstrap-datepicker/1.3.1/js/bootstrap-datepicker.js"></script>
<div class="input-daterange input-group" id="datepicker">
<input type="text" class="input-sm form-control" name="start" />
<span class="input-group-addon">to</span>
<input type="text" class="input-sm form-control" name="end" />
</div>
<!-- end snippet -->
I'll leave adding a button as an exercise for the reader, but check out how to style input group buttons in Bootstrap