Reddit is basically a large online forum, probably one the largest of it's kind and for me to describe it as a whole would be like asking me to describe society as a whole, it's that big.
one thing that makes it hard to describe it is that it doesn't have a specific theme or category but loads of them separated into different subreddit (subforums if you will) covering pretty much every topic there is; literature, movies, gaming, tv, cooking, coin collecting, countries, religion, politics, adult content, cute pictures, stuff that's mildly satisfying, revenge stories on both petty and pro levels, that one tv-show that was canceled over a decade ago, outdoors, stuff that only 14 year olds find funny, actors, AMA's (ask me anything) or just a big ol' echochamber (refereed to as circlejerks by the reddit users).
So do a bit of research on the subreddits and see that you find appropriate for you and your children before letting them loose on the site.
not intended for anyone under the age of 13
Reddit is a somewhat cleaner 4chan. That's good. It has a lot of stuff for everyone, from religion to politics to hacking to building stuff to conspiracy theories. I'd say that it is the front page of the internet ;).
It is a good, trustworthy site, don't get me wrong. You are at extremely low risk of harming your computer as long as you aren't clicking malicious links (moderator quality does depend on the subreddit, but overall they're pretty good for keeping malicious links off the site). However, the community is not the most egalitarian; it's all about your karma, registration date, and whether you go with the group mind. Be prepared to be relentlessly downvoted or have your posts deleted if you go against the groupthink of your particular subreddit.
Reddit is a great way to find stuff from all over the internet, but in my experience, I prefer lurking and reading links as opposed to being an active member.
PS: I do not use this username on Reddit, so don't go downvoting my comment on here if some other nerd with a similar screename made you angry.
Reddit is a site where users can post links to, comment on, or discuss nearly any kind of content or subject. Each subforum, or "subreddit" has its own rules, subjects, and moderators. Some subreddits are fine for kids, others are for adult only, most fall some where in between.