As far as the Finder window.. that's the name of the Home Folder and that can't be changed.... BUT you can just make a new user and go from there... after the new user has been working for a week or 2 with no bugs or issues... delete your sons user account. This is all done under System Preferences/Accounts.

"If it turns out that President Barack Obama can make a deal with the most intransigent, hard-line, unreasonable, totalitarian mullahs in the world but not with Republicans? Maybe he’s not the problem."