Who's This? The group of kid heroes occupying the top half of Who's Who vol.XIII's page 26.
How you could have heard of them: Not to be confused with the Fables character, the Golden Age Little Boy Blue had a son who was featured in a "Bonus Book" inserted into Flash #12 (1987) leading a second generation of Blue Boys, which somehow led to them getting an entry in a Who's Who Update (and then nothing). An apparently unrelated character with that name showed up briefly in Morrison's Seven Soldiers of Victory #0.
Example story: Sensation Comics #77 (May 1948) by Frank Harry (writer unknown)
Who else? I thought about the League of Super-Assassins, but knew all the members through their membership in various Legions. Not sure who else I'd like to cover in vol.XIII. Suggestions?