Amazon has decided to tighten up a bit on Prime security and perks. Until now, Amazon Prime membership has allowed you and four other members of your household (of any age) to share one account. As of today, that will change.
Amazon revealed that their new policy for Amazon Prime account sharing will be limited to one user and that user must be an adult. Furthermore, it's a bit more difficult to use multiple cards now. You will still be able to use other member's cards, but you will need to manually authorize each card.
There are also some stipulations regarding how children can use the account, so be sure to check out the source link below for more details.
Finally, there may be one bit of bright news regarding this change. It doesn't appear to be retroactive, and may only apply to new Amazon Prime memberships. We cannot seem to confirm this at the moment, so don't hold our feet to the fire if this changes.
Source: Amazon.com Help About Amazon Households