To protect their children from "Steam"Games
- Start "Steam". If your Client is not updated automatically, click in the menu bar, click "Steam" and then on "After Steam Client Updates".
- As soon as "Steam" is ready to be updated, go to the menu item "display" in the "settings"area.
- Click on the Option "Family". From here, you can open the "Family Options" by selecting "manage family options".
- Now children backup configuration and you can set some restrictions (see the Screenshot). It is a good idea in the first step, the options that are preset to maintain. Other persons to whom you entrust your "Steam"Account can't access your personal profile, as well as Community Features.
- In the next step, select all the games that may be played.
- To enter last, you have to enter a PIN. Only with this Code, the family options will immediately turn off. A red or green Icon at the top of the image to enable or disable the parental control from then on.

"Steam": The Parental Control
How to Steam without a credit card numbers, we can tell you here.