As we were building a Sermon Series layout, using a Parent content channel for Series and a Child content channel for Sermon items, it became apparent that there wasn't an easy way to affect the order that child items were returned.

The demo site on Rock uses a "Content Channel View Detail" Block to display Series information with a URL query parameter, but that Block currently doesn't support Rock Entities, so I rebuilt the content for the Series on that page with a "Content Channel View" Block, and a contentchannelitem entity to loop through and sort child items by Start Date in descending order (newest first).

@brian at NewSpring helped me with the attached Lava

<ol class="messages">
    {% capture childIds %}
    {% for child in Item.ChildItems %}
    Id == {{ child.ChildContentChannelItem.Id }}{% unless forloop.last %} || {% endunless %}
    {% endfor %}
    {% endcapture %}
    {% contentchannelitem where:'{{ childIds }}' sort:'StartDateTime desc' %}
    {% assign sortedItems = contentchannelitemItems | Sort:'StartDateTime desc' %}
    {% for message in contentchannelitemItems %}
    <li>
      {{ message.Id }}: <a href="/page/461?Item={{ message.Id }}">
        {{ message.Title }}
      </a> - {{ message.StartDateTime }}
    </li>
    {% endfor %}
    {% endcontentchannelitem %}
</ol>