I assume that you have done this by modifying the User Profile settings?
I haven't looked at that before, but you may find that all of that is exported if you export a template of the site. There is also this tutorial:DotNetNuke Portal Templates and the Site Wizard
I would suggest that you export a portal template for your site, then look at it to see if it includes the User Profile changes. If it does, then you should be able to work with the template to add it to your child portal.
But, depending on how much you have done, it might be easier just to redo this for the child portal.
It is also possible, using SQL, to copy the changes that you have made from the profile definitions and profile properties table and add them back with appropriate changes to the PortalID. You'd have to work out exactly what to change.
Whatever you do, I'd recommend doing this on a copy of your site before attempting it on a live site.