I have zero background in psychology, and only slightly more experience with children.
But as someone who was once a child, and who is consistenly confused by the media created explicitly for children, I wonder why it exists. In particular, is such media proven to be better developmentally for a child than, say, a relatively clean sitcom designed with no particular age group in mind? Or is "Baby Shark" better than the indie electro-pop on my iPod?
I understand why children's books exist-- they actually help isolate aspects of a language to assist with the reading component of linguistic mastery. But this principle doesn't extend so cleanly to audiovisual forms of media, since a child can more easily passively glean from such content (as they already do in day-to-day life when adults have conversations around them).
It would be awesome if your answer included some research-- being outside the field, I struggled to find sources myself.