By the K9WebProtection, I do not only mean filter from porn or the like, but also from phishing, malware and spyware links. It is very light and updates frequently on the cloud via its WebPulse.
Welcome to MT! If you have teenagers you can use K9WewbProtection or the same variant of Norton.
Personally I'd lock(prevent access) my main partition against any use. Create a partition for them only and install Returnil System Safe Free or if you have the bucks to spend the Pro version or the dependable Deep Freeze
You'll sleep better knowing that they cannot boink your system because whatever they do your system will return to it's steady state!