As far as social media goes, I just flat out won't allow it until they are 18. Not trying to convince you Noodle, but more to explain my perspective. Looking at our generation who didn't get a hold of it until well after adulthood and how retarded 99% of the population is with it, I don't see how it's a good thing to let children who don't know any better to have access to it as well.
Kids can fly off the handle and act before they think. So something they post today that is funny as hell, is all of a sudden extremely embarrassing ten years down the line when they are out looking to get a high end job. There are also legal ramifications too. Again, as someone else said, if they are under 18, any picture involving themselves in any state of undress, is considered child porn. And not only is your kid responsible as the recipient or trafficker of said child porn, you are as well if any of it resides on a device connected to your home network. Then you add in the social anxiety that social media piles on, and it's just crazy.
With that said, things that are like the old days of anonymous presence are all fine. They both have PSN accounts (under my parent account), and Roblox etc etc. As long as the world at large do not see them as my thing 1 and thing 2, and they follow my absolute rule of no real information is to be given out, we are cool. Then I have a basic web filter to keep all the porn at bay. If my son wants access to it, he has to earn it like I did and find some dusty ass VHS somewhere.