The Squadron of Justice was a modern iteration of a couple teams that debutted in the golden age of the 1940's, neither very storied nor as long-lived as the premier team on Earth-S, the Marvel Family. Still, they filled the niche of their world's Justice League/Society during crisises when heroes were needed.
Initially, the Squadron of Justice consisted of three Billy Batsons nicknamed "Tall", "Fat" and "Hill", each hailing from a different part of the country yet all having the same courage as their more famous namesake who broadcasted on WHIZ-Radio and TV. They all discovered the intrinsct ability to channel the same powers of Captain Marvel as the man himself, although modestly adopting the name Lieutenant Marvels, and as the Squadron itself.
Later, Captain Marvel Junior along with Bulletman and Bulletgirl were invited by Minute-Man to a private residential home for regular meetings to compare tales of heroism and valor. This assemblage was named the Crime Crusader Club, and while not actually working together on any cases (save one) they built bounds of trust and friendship. Similarly, on occasion Captain Marvel would encounter his one-time foe Spy Smasher, back to righting wrongs, as well as the Golden Arrow and Ibis the Invincible.
Most of these heroes, as well as Mister Scarlet and Pinky, were present at a Fawcett City ceremony honoring the Marvel Family, the same occasion wherein Sivana encased all present in Suspendium gas, keeping these champions preserved ageless for decades. Hence, when they were drawn together by Shazam into the Squadron of Justice during the mid-70's to battle King Kull (just like Shazam's counterpart Nabu aka Doctor Fate drew together the Justice Society on Earth-Two decades earlier), they were still in their prime. Still, the years wore heavily on most of them leading them to retirement.