Sort by date entered inside structure field

Hey there.
I’m looking for a way to sort entries of a structure field by one of its field values (which is a date):

events:
  label: Calendar
  type: structure
  entry: >
    <strong>{{summary}}</strong><br>
    {{description}}<br>
  fields:
    summary:
      label: Summary
      type: text
    description:
      label: Description
      type: textarea
    begin_date:
      label: Start
      type: date
    end_date:
      label: End
      type: date

and my template looks like this:

<?php $events = $page->events($own = true, $allies = array('children' => true, 'siblings' => true)); ?>
<?php foreach ($events as $key => $event) : ?>
  <?php snippet('event-teaser', array('event' => $event)); ?>
<?php endforeach ?>

Now I tried different things, like appending ->sortby(begin_date(), 'desc') to the $events definition, but nothing seems to work really … I replaced begin_date with different toStructure() calls and stuff like this to access the begin_date field, but I am stuck really …

This should work:

$events = $events->sortBy('begin_date', 'desc');

Totally, thank you (once again)!