JSFiddle - React, Tailwind, and code Playground

HTML

<label>London<input type="checkbox" name="London" id="checkbox"/></label><br/>
<div class="innerpost">
<label>N1 2AB<input type="checkbox" name="N1 2AB"/></label><br>
<label>E1 1AB<input type="checkbox" name="E1 1AB"/></label><br>
</div>

JavaScript

var element = document.getElementById("checkbox");

    var div = element.parentNode.nextSibling.nextSibling;
    if (!div.tagName) div = div.nextSibling;

alert(div);