We all had a favorite show growing up -- Hey Arnold!, Rugrats, That's So Raven, Sabrina The Teenage Witch (which will always be my favorite) -- but has the quality of children's media really been dumbed down, or is it just nostalgia? If it has, then why?
First off, what is nostalgia? According to Merriam Webster, the simple definition is pleasure and sadness that is caused by remembering something from the past and wishing that you could experience it again.
The idea is that, maybe, instead of children's media actually becoming watered down, we are subconsciously comparing them to our favorite shows growing up. While there are some really bad shows currently on television, there are also incredibly good ones that, in my opinion, are better than the old cartoons they had when I was a kid.
They not only teach children about life lessons, but also include diverse sets of characters, such as Steven Universe and Legend of Korra (although, to be fair, that was a continuation of Avatar: The Last Airbender). However, the question is "do the good ones outweigh the bad?" which is, honestly, kind of subjective. The parent of a child who watches nothing but quality television will say there are great kids shows, while the parent of a child who watched nothing but mindless entertainment will say it is bad.
The answer that I have come to is that the quality of children's television is more or less the same as before, with great shows alongside mindless entertainment. It purely depends on what you look at.