If the entire app was returned unprocessed, then I believe they do not consider you've submitted any app at this time. So next app (if accepted) will be considered your first one, so will not be able to include child 22 or over.
The only chance would be if the visa officer made some note on the return letter that your app was locked in already or would keep your initial submission date, and you just needed to re-submit.
What was their specific reason for returning it?