Reddit is a library attached to a dark alley. For an adult or a very mature older teen, it's an essential tool for information and community. For anyone younger, it's a liability.
There are no real training wheels here. The 'parental controls' are basically a pinky promise that the user won't click the 'Show NSFW' button. If you decide to let your teen use it, do it on a desktop in a common area and talk about what they're following. If they're just scrolling the 'All' or 'Popular' feeds, they're going to see the internet's id, and it isn't pretty.


