jQuery Simple Example

HTML

<script src="//www.addressfinder.co.nz/assets/v2/widget.js"></script>
<ul id="selection">
  <span><label>First<br><input type="checkbox" name="First"></label></span>
  <span><label>Second<br><input type="checkbox" name="Second"></label></span>
  <span><label>Third<br><input type="checkbox" name="Third"></label></span>
  <span><label>Fourth<br><input type="checkbox" name="Fourth"></label></span>
  <span><label>Fifth<br><input type="checkbox" name="Fifth"></label></span>
</ul>

JavaScript

$(document).ready(function() {
  $('input[name="First"],input[name=Second]').prop('checked',true);
});