Steam Families parental control at child purchase request features
4What games are shared? By joining a family, all games are automatically shared with the other members of your family. Adult accounts can use parental controls to limit which games each child in the Family can access. Basically, Family Sharing enables you to play games from other family members' libraries, even if they are online playing another game. If a family member plays your games they will have their own save. Note that if you would like to play at the same time the family member will need to purchase a copy of the game.
Full Video: https://youtu.be/Pr-71eJaKv8
Other Features, Steam Families includes new parental controls that allow parents to set limits on what and when children play games on Steam. Steam Families introduces a new payment option where a child account can request an in-family adult to pay for their shopping cart.
Is it available? To test the new Steam Families feature, you will need to have opted into the Steam Family Beta. Then any family members you invite will also need to join the beta. The adult can approve and pay for the purchase from their mobile device or email. Once approved, all games from the shopping cart will be added to the child's account.