If you want to know how Shazam! fits into the world of the Justice League, then you should probably ask Freddy.
Jack Dylan Grazer of It fame plays the foster brother to Asher Angel’s Billy Batson, the kid who says the word “Shazam” and transforms into the fully grown adult hero played by Zachary Levi. In this story, developed by Lights Out director David S. Sandberg, Freddy is the go-to expert for all things superheroes — and not just in comics. So he knows what he’s talking about.
As Levi explained to press visiting the Toronto set of Shazam! back in April, “The bulk of essentially, I think since the Man of Steel, all of that has really happened in our world.” So while Superman was battling Zod and then Batman and then Doomsday and then death and then Steppenwolf, Billy Batson was being tossed around the foster care system.
Source: IGN.com How Shazam! Fits Into the DCEU