Billy Batson having a crush on Wonder Woman comes from the "Power of Shazam" comic. That comic also had the Wizard communicate to Billy through a dream, where his face was on Wonder Woman's body.
The Daughters of Atlas do not appear in the comics. They are original characters created for the film.
Dwayne Johnson was accused of "kneecapping" this film by refusing to appear as Black Adam and instead producing the standalone Black Adam (2022). In the comics, Black Adam is the archnemesis of Shazam, and Johnson likely would've boosted the box office numbers. One insider even alleged that Johnson didn't like Shazam.
Darla adopts a pet kitten, which she calls Tawny. In the comics, Shazam had a talking tiger friend named Tawky Tawny.
Grace Caroline Currey, who plays Mary Bromfield, also plays her superhero form, replaced Michelle Borth from Shazam! (2019). According to director David F. Sandberg, Currey is now playing both parts but her hair and makeup are slightly different when she's super so her "normal" identity is kept safe.
Michael Gray: a previous live-action Billy Batson from Shazam! (1974), appears as a bystander in the final battle. Gray not only has on a red and yellow shirt, his costume from that show, but he calls Shazam his original title of "Captain Marvel".
Natalia Safran: wife of producer Peter Safran, appears as the driver with kittens. She appears alongside her daughter Lou Lou Safran.
Lotta Losten: Wife of David F. Sandberg appears as the first person Shazam saves on the collapsing bridge.