To reorder your compound object children, Manage the parent object and click the Compound tab. Under the "Reorder" section, you can drag around the children to the order you prefer.
If your ordering still isn't being respected, make sure you aren't using Solr for your ordering query:
Arca does not have Solr fields that index the compound sequence, because the use of these fields causes major memory problems when there are lots of compound objects.