Hi Chris,
You could potentially use the "Export Site Template" option available from "Site Management" to be able to export the original site. But there is a problem I see right away related to the importing on a child portal.
A child portal will have a "subfolder " structure, i.e. if the main site is www.mysite.com - the child will be something like, www.mysite.com\child - because of that you will have problems with image paths on the site as they will not get found because the new site is running under a folder. You may also have broken links all over the place due to internal links not getting found.
My 2 cents.
Cheers,
Aderson