JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://twitter.github.com/bootstrap/assets/css/bootstrap.css">
<div class="span12">
    <div id="DOB_picker" class="DOB_picker">
        <fieldset class="birthday-picker">
            <label for="birth[month]">Month</label>
            <select class="birth-month" name="birth[month]"></select>

            <label for="birth[day]">Day</label>
            <select class="birth-day" name="birth[day]"></select>  

            <label for="birth[year]">Year</label>
            <select class="birth-year" name="birth[year]"></select>         
        </fieldset>
    </div>
</div>

JavaScript

$("#DOB_picker").wrap("<div class='row' />");