Steam Family Options has exited beta and has been released into the wild for all users in the main client.
Introduced in mid-December 2013, Steam Family Options allows a user to control what content may be access by their young ones. "Whether a Steam account is your own or your child’s, you can use Family Options to limit an account’s access to a subset of its content and features. With Family Options, access to Steam Store, Library, Community, and Friends content and features may be gated by the entry of an additional PIN," an explanation reads.
Perhaps more importantly, it also includes the Steam Family Sharing feature which allows a user to share their library of games with up to ten others. Accounts authorized to access your library can "borrow" a game and play it fully, earning their own Steam achievements and saving their own game progress to the cloud.
For those who need help with Steam Family Options, there's a group on Steam that you can join where you can find more information.