I thought this was going to be easy; showing the order number of children against their parent, but the only answer I can find is in this thread
and I'm unsure how to implement this into my code.
{% for chapter in entry.descendants %}
<div class="part"><span>Part {{ chapter.orderNumber | numbersToWords }}</span></div>
</div>
{% endfor %}
Resulting in: Part One
Note: numbersToWords
is the Helpers Plugin by carlcs