Zen Account is a service made by Zen Studios for Zen OS. It's a way to keep an online backup of things such as bought games, a way to have multiple accounts on a single console, as well as a way to download games and play online. It's also used to download updates for the system, and if an user is registered as a beta tester, they can download betas of updates and games.
The service also works similarly to Miiverse , in that the user can post comments and drawings on the service. These are displayed in games and/or in the poster's Wall.
It's currently fully working on Zen OS.
Users can either make an account when they setup Zen OS, or online at zenstudios.com/account. To make the account they'll need to make an username, add their name, use a valid e-mail, and put their birthday. If the user is under 13, they instead get a Kid account.
Zen Account Kids is a variant of Zen Account. It works exactly the same, except that the user not able to apply for beta testing and they're not allowed to buy games (they can only download free ones). Also, the option to post/see comments and drawings can be disabled or enabled.
As soon as the user becomes 13 they will get a Happy Birthday notification and a notice that their account has been upgraded to a normal Zen Account.