title: Write meta_query for group fields in Advanced Custom Fields (ACF) for Wordpress
body: <p>I think the ACF docs are pretty sparse on how to query sub fields of a group made with Advanced Custom Fields.</p>
  
  <p>Example:</p>
  
  <pre>
  acf_custom_dates_group
  acf_custom_date_group_child
  </pre>
  
  <p>How would I perform a meta_query for values in the child field?</p>