Well, we know that childhood is extremely important to the development of humans, but we don't know what kids turn out to be if all they watch for years is just a bunch of colors that trigger dopamine and serotonin release constantly. Almost all adults in the U.S. today grew up with some form of media as T.V.s have always been pretty cheap one-time purchases (until recently with cable TV), so if you replace TV content (which at least always had a plotline or other educational content) with YT Kids they might turn out to be worse at problem-solving or other daily tasks that you need to perform for most jobs. It's definitely a subject that should be studied.