How old is your son? Someone has to be 18 to establish a publishing account.
Assuming he's an adult, you'll have to unpublish them from your account, and he would upload them as brand new books on his account. Be sure to let KDP know what you're doing, to avoid accusations of plagiarism or unauthorized copyright infringement. As long as you're talking to KDP ask if they will transfer the reviews over. This can be a somewhat messy process, but it can be done.
Quite a few self-publishers seem to publish other people's books, which generally makes me uneasy, but if you get along well with the lad you can probably continue doing so if he is happy with the arrangement. You'll either have to include the income on your own tax return (assuming you are in the US) or file a form 1099-MISC, which can easily be done through TurboTax and other software programs.
Otherwise, you can use the Contact Us option (bottom of this page, right side) to ask Support for help.
(If all the books on your account are his, then the easier thing to do would be to transfer the account.)
(Don't trust KDP to publish a print edition. Don't trust CreateSpace to publish an ebook.)