The setting that enables you to watch adult content is disabled by default. It can be enabled by going to Settings>Adults>Hide Adult Feeds and Applications and unticking the option box. To block others from enabling it, you can password protect it by going to Settings>Adults>Set Adult Content Lock and entering a password. This password will be required to enable adult content. From the Home Screen, select Settings > Adult, and tick the “Hide adult feeds and applications” box. It will prevent this type of content from showing on the menus.
Please note, this will only block the apps that Boxee provides by default. Adult content can still be accessed through websites and the local network (i.e. local storage)