I would actually start with the % of kids under 15 who consider themselves rabid baseball fans? Then I would follow that up with how many of those 15 year olds you actually know. Anecdotally, I don't know many of either, but my oldest is 5. Incidentally, I would think that a "rabid" 15 year old baseball fan would recognize the name Tony Gwynn or Reggie Jackson (retired 31 years ago) just as much as I would have recognized the names of Jim Bunning, Nellie Fox, or Early Wynn at that age. So like I said, it require context.
I'll also add that it's a different time. My oldest is 5 and he is not into watching baseball (let alone into the history) as much as playing. We went to the Yard Goats on Sunday. The game held his interest for about 3 innings. Then it was a never ending loop of, "how much longer until we can go the the bouncy slide?" I held him off for another 2 innings, IIRC. Also, I was speaking with his head coach who also runs the town tee-ball clinic league and he mentioned that they may not have the Tee-ball level, let alone the clinic next year due to dwindling numbers.
Finally, those guys you listed were either recently retired or on the "Amen Corner" of their career when I was a kid. Dave Winfield, for instance, was last relevant in 1993, a full 10 years before a 15 year old would have been born. It's sort of an apples/oranges because I have an above average WAR in terms of trivial baseball (dare I say general sports) knowledge, but in looking at the 1967 All-Star rosters (i.e. 10 years before my birth), I certainly recognize a number of names. On the other hand, who are Max Alvis, Paul Casanova, Andy Etchebarren, Gene Alley, Denny Lemaster?