Steam looks to provide safe environment with Family Options
Newsbrief: Steam users can now restrict their account when other friends or family members are using their hardware, using the newly-released Family Options.
Previously in closed beta, Steam Family Options allow you to lock down elements of the Steam client such as the store, community elements, chat and online profiles, such that young children, for example, can play games with less for parents.
You can also choose to lock out specific games, simply using a PIN-style passcode. The options can be found in the main Steam settings.