are you shure that we can delete the IP Portal from the list, it is not a alias, when i create the site, there is nothing on alias
Go to Site Settings, and scroll all the way down to the end, you should see the portal alias there... if the existing portal alias is the IP, the add the URL version as well. If not then we may need to resort to something else.

can i have a IP public nated on the IP point to the child url ( is it possible to have a IP for a the child portal)

Yes, it is possible, you can create the portal as a parent portal, and add the PortalAlias www.yourdomain.com...

That is interesting...

If you really must, you can change it directly in the DB table PortalAlias.