I don't think it's (always) about being obsessed with social validation though, it's a new societal norm brought about by social media. In fact it's the _hook_ it's why people use social media at all, because you can _share your life_ with people in a way that wasn't possible before. The raising of children being a major part of that life. I would go as far as to say that the children aren't actually the subject in these posts, the real subject is the parent's life and the posts containing images and anecdotes of their kids are a side effect.
Maybe this is an opportunity for some social media company to get ahead of this and use facial recognition to tag people across ages. If the user decides that they don't want their image to appear on someone else's account, they can go through the images granularly and take them down.
I think what I'm getting at is that this is _new_. It's as new as is the ability of a 14 year old to express their frustration with something and have an audience of millions. I don't think the solution here is to tell parents that it's inappropriate to post about their children online. I think the real solution has more to do with finding a comfortable balance and set of controls so that everyone's interests can be accounted for.
p.s. I shuddered while typing "14 year old to express their frustration with something and have an audience of millions". The next 50 years are going to contain some _hard_ times.